The game starts of at a reservation on the planet earth. Strange things happen and you and other people end up on a space ship with an alien form.
The game play is excellent. There is no real "floor" and ceiling, but the gravitation might chance depending on your actions or where you are walking. Not only does the game play around with the gravitation a lot, but also with portals. There are different kinds of them, some are clearly visible, but some are hidden inside boxes, for example.
Besides the wrench from planet earth, all your weapons are taken from aliens. Seven weapons that you can use, includes the wrench, which is as good as not used through out the whole game after you get your first real weapon. All weapons have two different firing modes and are used differently according to mode used.
You also have a special ability, spirit walk, that is used to solve some puzzles in the game. When in the spirit world, you can also sneak on enemies as they will not be able to see you while unless you attack them first.
The biggest issue with this game is, that it is short. It took less than 6 hours for me to finish this game. After finishing the game once you'll gain access to a harder difficulty level, but it does not change the story therefore it does not have a real function making the game "longer". Another one was, the multiplayer which at the current time is as good as dead. I tried looking for servers few times, but I never found one, so don't count on the multiplayer at all.
I also had some issues playing this game in Vista, but all of those issues were solved after a re-install of Vista. There might have been something messed up with my Vista installation, but from what I read there have been more or less a lot problems with the game. Especially with the OpenAl sound, but I had a great experience with OpenAl sound, so I can't support that opinion.