For the next ~44 hours from the time of this post, you can get
Mount & Blade for free (and DRM free!) on GOG. And all the other Mount & Blade games are 75% off as well.
Supposedly M&B: Warband is the best of the bunch.
I've played quite a bit of M&B (the original) but haven't really played any of the expansions/sequels.
And here's a roundup of some mods for the game which should give you plenty to do:
http://www.moddb.com...00-free-limited-time 
