Super Tux (Game)
Windows XP, Windows Vista, Windows 7, OS X
This game will probably be considered great by some and far too derivative by others. Quite basically, it is a Super Mario clone in a penguin suit, complete with icy backgrounds and enemies to match. In many respects it plays almost identically to Mario - everything from the 'growing bigger' power-up to the poles at the end of each level are duplicated. Even the old 'my girlfriend got kidnapped - I have to save her' storyline is used.
The good news is that, while the gameplay doesn't stray from the Mario formula an awful lot, the game itself does have a lot of polish. This is more than can be said about many of the 'faithful' Mario clones, which both look and play rather pathetically in comparison to this. The graphics are beautifully drawn and the animations for the various enemies, which include bouncing bombs and ice-cubes, is excellent.
Another wonderful element is the fact that the game has so many levels. While most freeware games usually provide somewhere between 1 and 10 levels, this game contains a lot more and the level design itself is quite creative at times.
Aside from this, the game is super-smooth and the controls are as responsive as you could hope for, as is the collision detection. This means that if you get frustrated at all during this game - it's not due to bad coding and you only have yourself to blame.
Overall the good seems to outweigh the bad - it is just unfortunate that this couldn't have stamped itself with its own brand of originality, rather then borrowing so heavily from somewhere else.