I think you're all forgetting this game is over a decade old...
It's a great game. The mechanics work great.
The only issue I've ever had with this game is the fact that it feels too slow.
The levels are actually quite easy, just... really long. (The first level is nearly ten minutes.)
Achievements and upgrades make grinding a must for this game, which it seems few people realize. Other than the grinding and slowness, my only other issue with this game is the singular sound track, which gets kinda boring real quick. A few different options to switch things up would be really great.
Would love to see this classic game remade, or even a sequel, if the creator is still around.