there are a lot of complex good games out there, but one of my continual favorites has to be ProGammon, which you can download for free off Aminet - that game cheats like I don't know what, but once you've endured playing a computer that cheats like hell, you can beat any human player VERY easily.
This assumes you like backgammon, of course

The reason why I say the game 'cheats' is that invariably you are about ready to win and the computer somehow manages to roll 3 double-sixes and put all his pieces in before you at the last second. There are other examples but this is one of the most infuriating. Thus you have to be REALLY GOOD (or really patient) to beat the darn thing!
kevin orme
amiga university
www.amigau.com