If you are at all interested in the Alien franchise, you must pick this supplement up.
The system is pretty simple, and keeping with the DIY philosophy of ICRPG, it is more a system for setting up a game than it is an exhaustive lore book of useless alien information. What you get: a system for running Xenos independently (think, no GM necessary), a simple process of "commando" creation, tables for mission objectives and mission escalations, pregen characters that serve as a kind of class system, complete with preestablished loot and milestones, a vehicle system (inlcuding a lift truck to really get some Aliens vibes going), and a stupidly huge amount of art assets, that, frankly, pay for themselves if you do any amount of VTT.
I will say a couple of things: I do recommend you get the ICRPG Core and Worlds to flesh this out some if you are looking at this as an RPG. You could absolutely use this to run an entire DIY Alien-themed campaign, but I think you'd have a better time of it if you had access to the sci-fi loot and other ICRPG goodness. I will also point out that this is definitely meant to be either a "runs itself" kind of board game or as a "DIY RPG" so don't come in here expecting an "on rails" experience. Personally, I prefer that, but if you're looking for a "do this, then do this" campaign module, this isn't it. You're getting a guidebook, ruleset, and system for creating a campaign or one-shot, which, in my opinion, is 100s of times better.
To sum it up, like i said in the begining, if you love Aliens, this is custom-made for you. The VTT items are worth cost on their own.
[5 of 5 Stars!]