X-COM The Enemy Within, for Android
This Android port of the console game is flawless. I actually like the UI better on my phone than on my PS3. I have had the tiniest of technical glitches (one crash to date) - also better than on the PS3.
Killer on battery, but that is not unexpected. And maybe for the best, for otherwise I'd likely waste my whole life on it.
Would not recommend for a screen much smaller than mine (Samsung Note 2).