I finished XCOM:Apocalypse and I have to say, that besides Jagged Alliance 2 it's one of the best games I ever played on the PC. GET IT!!!
As for UFO:Aftermath, this one was really bad, I have UFO:Aftershock now, and I'll give it a try next week.
And if you like those turn based combat games, get Silent Storm, it's really good, but also tough to play, not for beginners.