I've been playing a game called Auralux and it's been good. The premise is simple, take over the galaxy while eliminating your opponents.
"Auralux is an abstract, essentialized, and simplified real-time strategy game. You command only one type of unit and have only one type of order to give those units. Quick reflexes will get you nowhere. The only path to victory is through clever strategy."
That's not quite true. There's a good timing involved, so quick reflexes do sometimes matter. The strategy is somewhat less than highly complex - basically maximize your population and create defensible positions. Still, it has an elegance and its own complexity arising from simple rules that makes it fairly compelling.
The hardest level, I think, is Clash, earning an "insane" difficulty level from the game creators. I had beaten every other level but I couldn't beat this one. For days. Finally I beat it and since then, I've come close but have never again won.
It's too bad that I didn't know I was winning until late in the game and didn't take intermediate snapshots. Still, for the record here's my win. I'm Blue and I started with only one position at center bottom. Red and Green started with 5 positions each at left and right. Larger positions have a higher generation rate, so they are more valuable.
Late in the game I've already eliminated Green and I'm started on Red. At this point I suddenly realize that I ought to memorialize the game.
Below: not from a win, but from a game when I followed a similar strategy. In this game I let Red get too many positions and Red won.