http://www.hurrican-game.de/Closest thing to a direct download:
http://www.poke53280.de/download/download.php?id=9This is a remake of the classic Turrican game. It's pretty much the best retro remake game I've ever seen; the graphics, gameplay, and level design are all awesome. It's also quite a difficult game, so be prepared to die a lot.
The main game isn't that long, but there's a level editor.
I don't know how exactly to describe the gameplay...it's a platformer with a lot of crap blowing up, gameplay is somewhat reminiscent of the first two Duke Nukem games, but a lot more varied and modern. (The crap in question is robots and fish, so it's not really "violent" in the hide-the-game-from-your-parents fashion.)
The game runs under WINE, but you need to do some weird crap to get it working. Check its AppDB entry (basically when the game "hangs" at the end of a level and when you start a new game, you need to start another instance of the game...a bit more complicated than that, but just brute-force trying again and again should work).