Android XCOM has been a mixed bag so far. At first it was very crash happy, crashing more often than not whenever a video clip would play, and a couple of other events too. I had to abandon my first game where I neglected to turn off the tutorial; one of the videos that play during the first mission would crash the game every time. I tried at least six times. The game is slow to start up, just like the PC version, so I felt like I was spending more time booting up the game than playing.
However, today my experience has been different. I've had far fewer crashes, and it's mostly been a joy to play. I have to wonder if it crashes more frequently at low battery levels or something.
The phone runs rather hot after playing for a while, but I've not noticed any correlation between temperature and crash frequency. Using my "infared" thermometer, I measured the back of the phone to reach a peak of 52°C. Quite uncomfortable to hold. I recommend putting the phone against a cold surface while playing, to emulate a heatsink.
The game is a very good port of the PC version. It is beautiful, looks almost entirely like the original. Some minor issues, such as the soldiers looking a bit out of place (they sometimes seem to have different lighting than the map they are on) and incorrect audio during some of the Skyranger landing animations) don't really detract from the gaming experience.
One should note, however, that this is just XCOM: Enemy Unknown without any of the add-ons. Not even the Elite Soldier pack, so you'll have far fewer customization options for your soldiers. You can't even change their armor color, and you lack the extra hair styles added, including the classic XCOM soldier hair that the Elite Soldier Pack added, as well as alternate armor appearances. So it's not really an alternative to playing the PC/console versions, but more a game to turn your Android phone into a mobile gaming console.
Oh yes, and the battery drain is about what you would expect; carry a mobile juice pack or the like if you play more than a mission or two on the go - you wouldn't want to run out of battery before you get back home just because you wanted to have some fun during your commute.
Recommendation: Hold off on buying until some of the bugs have been patched.
ETA: The game takes up a whooping 3.7 gigabytes and will of course only run on newer devices. Perhaps in an attempt to reduce bloating, you are limited to having only three ongoing games, and each of those are allocated four save slots, and one additional slot for the autosave.
Anything I forgot to mention or any questions you have? Comment!