I've started playing Battle for Wesnoth a little. Seems fun so far.
Will see whether I can gain some experience and hold my own on a level higher than "easy" :) Apparently, "medium" is supposed to be challenging-but-not-difficult, i.e. more rewarding without requiring five years' experience.
I really like the turn-based nature, since I've always found real-time strategy games too fast for me.