Your gameplay is pretty solid already, I will focus more on the bad things that on the good things so you can correct it, but there's lot of good things in here, it's pretty fun already.
About game design:
The first big issue you need to fix is: No feedback for the tomb being "passed" (if the player took the right shape), you should make an animation to show it's good, not just make it disapear, it feel weird and also make your gameplay less intuitive.
Second thing, I think the game should just start when you chose a (good?) shape
Well, actually, the problem is that, at the begining, if the player didnt read the "how to play" thing, it's not so intuitive, it feels like "omg its moving what should I do". It's really moving fast at the begining, it should really start slowly, and quickly be at a normal speed, and then slowly accelerate.
Also, a suggestion that might help with the "not intuitive" thing: Did you think of a health system? I find the game pretty hard for what it is.. I guess you should have like, a limit of 3 bad shapes or something like this. In that way, if the player makes a mistake or didnt understand, he'll be like "oh I need to take the shape of the icon on the grave! Okay I wont be hurted twice!".
And so you could also add power ups like "+1 health" or "-1 health" and there could be more and more "-1health" so it'll be more difficult.
Talking of power ups: Is it really good that the player can actually know if it's a good power up or a bad one?
I'm really not sure about it. At least not the way you did it.
the first problem we have is like "the player will never take bad power ups"
it seems that you fixed it by making the player obliged to take it sometime, if the power up is placed in the same place as the shape he need. It's really a cool mechanic, and that's something I think you need to keep. Buuuut: it doesnt happen so much. I think there should be more and more power ups on the screen, and it will be more and more bad power ups maybe. Well it's worth to be tried.
Also I think it could be good if there was power ups that you dont know if they are good or bad. Like a grey "?" or something.
You should really think about this, and maybe of other way to make situation in what the player has no choice but to take the bad power ups.
About sound design:
There is no music in the menu. It's kinda bad. It would just need a bit of sound, it feels empty.
Btw the music of the game is really good, you made it yourself?
Little thing, not really important I saw: When the game is paused, there's no "lecture" icon, it just the same icon than the one to pause the game.
Oh and fun thing: You didnt even mention yourself in the credits. Ahah
I hope all of this will help a bit, As you can see I'm more a game designer person than an artist or composer, and I've said lot of things, it might look like "omg your game sucks" but it really isn't. You know a mecanic is good when no one complain about it!
I know it might be a work in progress, but that's why I'm pointing up bad things, so you can correct it or at least think about it, even if you already maybe know all this and are working on it ^_^
Anyway it's already pretty good, but details is what make good games.
Have a nice day!