Pretty cool prototype!
Good points:
* I think the instant audio-visual feedback of clicking on a stone makes you definitely want to click more stones.
* Having different shapes AND colors made them very distinct.
Suggestions:
* I had the same "bad stone" (green) get chosen multiple times in a row, which made it less interesting... and I never actually had red chosen, ever.
* I felt the gamespace was too big for the gameplay. It felt like maybe it would be a good match for mobile, since it has simple gameplay and a smaller resolution might be nice to make it feel more crowded without feeling too simplified.
* I wasn't really sure how well I was doing, and in fact didn't notice the timer until it was at 2 seconds. Maybe some kind of positive feedback for combos, or progression mechanic with levels and experience (Level Up!), etc, could make it feel more dynamic?
* I wanted a stronger/bigger/in-my-face penalty when I messed up. Instead, I wasn't even sure that I DID mess up, when I made a mistake.
* Probably obvious and planned already, but you reeeeally need some menu art. The pixelly gems are OK, and the chiptuney music and sounds are OK, but even just changing the black lines to blue could make a big difference?
Good luck!
I hope your professors like it!