Many of you have probably already heard of Battle for Wesnoth. I tried playing it awhile ago and somehow just didn't get into it. A few days ago however I gave it another try and I am actually kinda surprised that the game is of pretty good quality despite being free.
Basically its a turn based strategy game or rather like a war game. I am impressed by the amount of campaigns and story lines though. There is no one single campaign but rather many many campaigns that all tell stories about Wesnoth. But the storyline doesn't get in the way either, its just good dialog and then well designed maps.
The other thing I like about Wesnoth is that the gameplay is kept simple and easy to understand and yet it has plenty of depth for those who like to get into the real strategy aspects of it.
Well those are the reason I am having fun but if you want to know more features it has, which are plenty, here is a link.