Battle for Wesnoth is fantasy strategy game. It’s not quite on a part with Diablo or World of Warcraft but still pretty good and continuously being developed further by the community. The usual story … orcs, elves and men! Since it’s an Open Source game, trying it out won’t cost you a thing!
There are the usual playe modes, campaigns or multiplayer. You can also play multiplayer games against the AI, by the way.
There’s nothing weird at all about installing it so the only thing left to do is to give you the link to the donwload page.