Good for a few minutes
Needs more new features tho, just release a "level pack" edition instead of a sequel. I can just think of a "Combo" system, the faster you burst the pieces the more you fill the combo bar which slowly depletes, and that adds multipliers... or stuff like that, you know, I think just focusing on the time is a bit limited (and I'm not a score-maniac)
I found a glitch where if you fail and keep moving the mouse like crazy after that, you can pop some pieces on the next level before instructions appear and clear the place a bit, or you can fuck up and lose another 20 seconds for nothing, which can be annoying if you don't do this on purpose (I wonder why would anyone). If you do it "right" the timer keeps counting, the trick is move the mouse kinda fast right after failing, and it doesn't work twice in a row, but you can do it over and over again.
Also please add a "Replay" or "Back to Menu" button after Classic mode!