Let me give you a hand: I'll review this by stating the most important points that stand out to me. I know it's an year old.

Bad things
– As others have hinted, it starts out dubious as it's not made very clear that there is no additional control or mechanic other than moving with the movement keys. Clarify it in the description? Saying that "They will step on you to get higher" didn't quite make it. Maybe "Think carefully: move and carry them whatever way you can" instead would be better. It's confusing (and a fail) to have hands in a game where you can't grab or hold. The identity that speaks along should joke about this.
– Without being too detailed, the order of the levels just seems screwed up. After the initial harder ones came some very easy levels that I beat right away. (It could have been due to learning how to play.) This is disappointing later on and discourages people from sticking to the game at the start.
– Pushing stuff isn't very consistent. You should have sorted out how pushing works under all scenarios as well as the overlapping bugs that there are. Removing a hand from under an object and sliding another object underneath it with the other hand right after is possible with some objects but not with others, which doesn't make sense. It also causes overlapping bugs that someone already mentioned. With a hard game that's supposed to have players looking for obscure ways to beat it, you should have sorted out all the possible interactions. Plus, it's a simple game so making sure that it's working consistently and without bugs isn't much work or asking much.
– I couldn't tell when the arms were stretched to their maximum and it harmed the gameplay.
– The level selection is interestingly nice but the navigation is broken. In a game I always want to be able to return to the main screen at all times. On the ending screen, there are no navigation arrows and it's impossible to exit. I have to restart the whole game to get out of the end screen. Terrible. The mouse cursor doesn't turn into a hand when hovering links, breaking a standard and creating a clickbait-like ending. I didn't mean to open your website, I just wanted to exit the end screen and check out some other levels again. Plus, the levels aren't numbered. I can't refer to them or know how many I beat or how many there were without counting – bad.
– Despite probable strong opposition to this view, the graphics choice is awful. Retro is cheap, overdone and looks horrible. This particular puzzle doesn't really justify it's use. It would look much better with a certain sleek modern artwork that I can only imagine myself. It's not the cartoon type.
– You should use the Newgrounds advertisements API in-game so you could profit from it. Also, developers can't excuse any poor quality in their games by saying that they aren't paid to make them when there's an API.
– A level creator (as in the game Tentacle Wars) would allow everyone to find more quality levels, as they would be up-voted. But I don't really mind too much that there isn't one. Although on the other hand, Sokoban games almost always have level creators.

Good things
– It's an epic premise playing with the two expandable arms.
– This original genre derived from Sokoban is awesome. Maybe it hasn't even been done. It's really great. It's a whole new game.
– The level design is good. So many games with bad level design, but not this time. Also, as someone else already said, it's challenging without having brute force difficulty like a pixel hunt, button smashing or a giant layout. This is further seen in how the arms' length was kept the same throughout the game. If it were someone else with the typical brute force difficulty, they would just make a big level with very long arms. But not this clever author. Good work. It felt so nice figuring out the first levels! The logic was just so sweet, really good.
– All games should have secrets and bonus things. There appears to be only a little one here that may have been unintentional, but that I still like very much. Throughout the game an identity antagonizes the player. In the final level, the walls resemble spelling out "FU," an initialism that ends up meaning "screw you." It's not explicit though. Subtility is very witty. It's boosted by the ending screen right after having "END" spelled out with the walls, establishing the context of writing with them.
– The game has several other nice touches in addition to that one. It turns black and white after loosing. It displays the word "reset" briefly when resetting. Far better than the popular hideous transitions that other games came to have. I wish, however, that the word "reset" would appear for as long as the R key was held. It's downloadable! Thank you very much for caring about that. Host the download at Dumping Grounds so that when your website dies it's still available on Newgrounds. It starts playing on the actual main screen! It has that nice take on the arms' movement sound. It has no introductions or fake preloaders starting right away. It has the improper entries, like Play and Forward, of the right click context menu removed, but leaving the useful ones, Quality and Zoom. Only the naive disable everything and put an advert in their place. Don't forget you can build Mute into it, the right click menu. These are all good things. We have a witty game designer here. The author of this game should definitely check out the game "You Have 8 Bricks" (ID 654221) to find similar creative and professional game design elements.

A fine game

I will try to provide constructive criticism. Let us see how it goes. Ignore the low rating, it means nothing.

I liked the game but I would not have played it if it had no medals. It did not catch my attention. You just jump around. There is nothing interesting to keep me playing. I do not care about scores because hackers and really good players ruin the fun. Scores are something from the past. Now people are into things like medals and achievements. So I suggest you to had more. Examples include reaching a certain height without double jumping or shooting every small block that appears until a certain height. Now those would be some good challenges/medals. Something to keep people interested. Not to mention the best thing would be actual levels and variation... You know, a full game? This is more of a mini game. (Nothing compared to the greatness of Tetris by the way.) My main suggestion is for you two to make a complete game with everything you can think of. Probably more important, it needs something to keep me playing. Whether it is levels, medals (you can still add them) or something else. I am not saying you did bad, the game is OK, in the end I liked it to the point of reviewing.

As for the artwork, I do not like "pixalated" graphics but this is different. I like this style. The colours fit well together. I have no major complains except for the font and the variety of blocks, backgrounds, and so on. I had trouble reading the text, it was too small. Newgrounds has an option (top right corner buttons) for the game resolution to be expanded. You could make use of that. But it is "grayed" out...

As for the coding I unfortunately can not help you, I can only point out bugs which is not so useful. I found several. If you are interested in knowing details just ask. There are problems entering the players' name, blocks smash me when they do not even touch me, later on the game the blocks stop being aligned and start being supported in the air, a tower is usually formed on the left and so on.

Since this is a simple game the game-play is also simple. I would like the game to start right away after I press the Space bar, I would like to be able to shoot while jumping. I would like customization of controls too, something that all games should have. Please consider learning how to do it so you can include it in all future games. Due to the variety of keyboards and styles of playing you must provide an option to change the controls. Other than that the game-play seems fine.

The music suited the game so well. You should have included it in the credits. Everything is to be credited. I would want a longer theme if the game had more to it. I suppose the sound effects were OK but the jump sound is annoying. All games should also have separated options to turn off sound effects and music instead of both together. At least you do have one option...

I enjoyed details such as rocks falling in the background with the screen shaking and dust when a block settles. The signs at the start are good, there should be more. I would want to go higher just to read them. Something bad is the pause system. You did not make it. I have seen the same pause system in other games. It has problems. The game unpauses automatically (causing me to lose) when I return to the window. It is annoying because it does not do what I want. It also looks too much "pixalated". P to pause is not in the instructions.

Well this is it. Focus on anything I said that does not apply to this game only so that maybe you could improve in the future. Sorry that I pay too much attention to details. I even tried not to mention them all.

Good work.

Here's my attempt at reviewing...

First of all, I don't want to rate this game, but since Newgrounds forces me to, I had to come up with something reasonably fair. Ignore the score.

I played this game and I kind of liked it. Fancy graphics with spicy music. The game relies on scores and achievements. It's good for those who like to compete for a high score and for those who rather try and get some achievements. But there is a problem with the latter. Many of this game's achievements aren't good. But I see you are accepting ideas and improving. An achievement is a challenge or an accomplishment, it was not a challenge for me to start the game. You created an achievement for that which I think it's lame. There are other achievements that I disagree with, such as the ones for winning other achievements. Those are pointless "fill up" achievements. Instead, you should have made real challenges that reward skill and cleverness. Even if that means having less. It's better to have only a few good ones than many bad. The Triple Tap or the Twinkle Toes, those are good achievements. Another good one would be one for jumping in the last moment (just before falling) or one for jumping over one track without landing on it. If you think hard you could come up with good ideas, not dumb things. Also, when I played the game for the first time I got so many achievements all at once and I barely did anything. This is so wrong. No effort is needed to win pointless achievements.

About the rest... There are common problems, nothing I haven't seen before. The game lacks more stuff, maybe diagonal and curved tracks among other things. This is not a real roller-coaster this way. :P The direction could also be from right to left instead of left to right like most games. You know, expand the game otherwise it's not really an "original spin on a classic concept" and not much of an epic coaster, not at all. You, just like many other, made the mistake of releasing the game before completing it. You are still improving the game. I understand you want feedback but now it's a mess with all the versions in different websites. Lets enter in details: there is no pause button. But I guess that is to keep things simple. Well, if it is a one button game than why can't it be any button? Although 3 options (what I found) is fair enough. The sound and music buttons aren't separated giving the players less options as well. (And the icon doesn't even change when clicked. Lazy.) In the Play Again screen, you could add the distance reached next to the score. I sometimes like to know but I can only see the longest one. There are also some unanswered questions... What causes the jump? Jet packs, springs, magic? The game goes on for days, how about some food dropping from the planes for the starving people? Silly stuff.

I found what could possibly be some bugs or just more things that don't make sense. In the instructions it says that if I land in the edge of a track I get a perfect jump bonus. I did land in the edge (the edge to the right, not the obvious one) and I got no bonus. There should be a perfect jump bonus for landing in any edge. Other bugs were fixed in other websites... Well done. Developers don't always care.

Now some good things. As I already said, the graphics. They are good and an important part of a game. Something you could be proud of maybe. The idea is also cool, epic coaster, not that epic but still nice. And you used day and night in your game. That is a great thing to include in a game, it's original and gives a good feeling. You managed to create this sparkling and blinking theme for the game, once more, giving it originality. Finally, the game starts in the menu itself. Usually the menu is in a different screen, separated from the screen where one actually plays. But not here, I like it.

Basically, I would expand the game, add proper achievements and pay some attention to details. Keep on it.