Battle for Wesnoth is a turn based tactical game with a huge variety of campaigns and unit types. Once you figure out the basics of this game, you will start to notice the depth of the strategy in this game. In the campaigns, for the most part, if you keep your units alive, you have them for your next mission with the experience they gained from all their previous missions. The tactics in the game can get very interesting, with things such as zones of control around your units as well as choosing how to upgrade your units. This is one of my top picks and a definate must have game.
Battle For Wesnoth Youtube, Battle For Wesnoth Trailer, Battle For Wesnoth Preview
Download Battle For Wesnoth