Diablo

One of the best computer games I have ever played!

Lots of action, with some RPG elements thrown in to make it more interesting. The game was designed to be almost endlessly re-playable. The whole fun lies in building up your character, making him/her more powerful, learn powerful magic, find better weapons & armor, and unique treasures which will help you defeat the demons & monsters of Hell itself.

By the way, although there are 3 character classes to choose from, I recommend playing the sorcerer. He is by far the best character in the game. He starts out the weakest, so you have be more careful than you would have to be with the warrior or the rogue, but eventually (after finding certain spells) he will become the most powerful character of them all. Besides, playing the sorcerer is also the most fun, since it allows you most control over the various spectacular magic spells.

BTW, read the manual. It's not only informative, as it should be, but it also provides lots of background info, which makes for great reading.