There were some iffy moments when the game would freeze, but it was easy to fix and I didn't lose any information, so it didn't really bother me. Some parts seemed hard trying to push through, but it was easy and quick enough to beat, so I feel the difficulty was pretty good. Not too hard to make a person extremely frustrated, but not too easy that it poses absolutely no challenge.
Overall, it was really fun. It's a great game to play if you only have a little bit of time (like between classes or something). I also like how you play as the alien, not a human trying to kill a bunch of aliens. :D
The appearance was also extremely good, I thought. I particularly enjoyed the look of the game and how it was set up.