Atomino

The Good
This game is a masterpiece. The graphics are very well done (of course there are not that much). The soundtrack (at least from the versions (C64, Amiga) I know) is great (especially the Game Over tune :-) ).
Gameplay is very well balanced. The game's difficulty increases with the complexity of the molecules you have to build (remove, rebuild) not by endlessly increasing the speed. With a little practice you can survive for hours (doesn't mean that you'll get a high score in the end, though), but a good game is not killed as easily by a single fault.
And no, it's not Atomix. At first glance they look the same, but it's really only the look.

The Bad
Nothing (and I don't regret the sleep I lost). Breaking one's highscores can get time-consuming :-)

The Bottom Line
Great think-puzzle-tetris-style game where you juggle with atoms until you see electrons circle around your head.