It's alright for a prototype and unique enough that I can say it would be cool to see the final product. While there are a lot of improvements that should be made, the biggest thing I'd like to see in the end is more fluid controls. Moving the blocks was really fidgety and awkward and with faster, smoother movements would make the game much more enjoyable.

A simple concept that could be really fleshed out. Hopefully the game will be a lot less buggy.

this has the potential to be a really good game when its finished. nice job.

could be a really good game, waiting to see the finished product

It's pretty okay for your first game. In my opinion, I think that if you made it a bit more difficult and added a lot more 'obstacles', then it would be even better. Also, my ears were sad the whole time since there was no sound; No victory chime, no BGM, no sound effects on death, no "point's" to collect, there are a lot of things that could make this great. For example, here is a list of features that I personally would like to see in the future:

Friction-Make it so there are surfaces with different friction, and make it so that the movement isn't so choppy (when you stop moving, gradually slow down to a stop); This will make the game feel more dynamic

Points/Coins-Make it a point that in order to beat the level that the player must collect all of the points, as well as avoiding obstacles.

Moving obstacles/enemies-This is way too easy without it; You could implement enemies with guns (or an automated cannon-type thing), lasers, etc. Be creative.

speed-The speed is really, really slow, and way to easy to beat it all. It should be much faster, and with the friction, it should also be harder.

Lack of artistic vision-I like the titles and everything, But the in-game art felt really un-inspired and was quite boring.

MUSIC-The most boring part of this was the lack of music and/or sounds. I would like to hear a victory chime, some BGM, sound effects, anything really, even if it's chiptune with little bloops and buzzers, it will really change the feel of the game.

All in all, this game is just a prototype as you've said, but if you could implement any/all of the above features, than this might be very good. Also, take some inspiration from 'The impossible game', it has all of these features, but lacks the dynamic dual-minded thinking needed here, which could actually make this game surpass it, potentially. Also, for the levels, Start off easy like a blank room with only one coin thing, and tell the player that in order to complete the level that they must collect all of the coin things and join the twins together, then go on to say how obstacles are involved, then go on to say how there are gaurds/enemies that will kill you if they catch you, and potentially have the guard-enemy, if they see you, chase after the closest one (albeit slowly at first), I don't know, just an idea.

P.S., If you need some music/sound effects, I'd be happy to help :)