I can't seem to review Enemy within by itself, so I'm putting this here. The original game is in most way a very good game. By itself, I'd probably give it a 8. This is more about the expansion though. I bought the expansion on steam sale. It's been a couple months now, and I still can't play it. It freezes all the time to the point of being unplayable. There no good suggestions, there is no fixes, and no word on a patch. I've update hardware, drivers, even tested on a completely different PC, same problem.
Now, lots of people can play it without much problem. Others can't play it at all, and others have my issue. I've given them amble time to deal with the issue and not even a peep about a fix on the way, just an ever growing thread on the steam forum about issues and frankly I feel ripped off now, even at the discounted price I got it at.
My advice, if you have a console, get it there, it will probably work. Avoid on the PC as you're just playing roulette on whether it will work or not.