Overall, this RPG is pretty excellent, and I would highly recommend it.
It uses a slight modification of the elegant and tight Mutant: Year Zero mechanics where you can push your character to re-roll a test, but they gain "Stress Dice", which improve their chances of rolling a success but also raise the risk of panicking. The stress system is incredibly good at evoking the slow, rising dread of the Alien films at their best. The fluff and lore encompasses almost everything from the first 3 films, the books, the comics, even some of the toys, leaving any contradicting canon to the GM and their preferences. The map of colonised star systems is huge, and only some are detailed to any great degree. The setting goes for broad strokes; There's enough detail on factions, corporations and governments to get by without having watch any films, but it is extremely helpful to have read some of the books or comics to get extra detail, or you can simply make something up to fill the gaps. This actually plays to the setting's strengths in a way, underlining just how vast the galaxy is, and how little of it humanity has actually explored.
Character creation is quick, based on starting archetypes such as Colonial Marine, Pilot, Corporate agent and so on. The equipment and weapons list are comprehensive, and include all the bits and pieces from the films from motion trackers to pulse rifles. While it isn't essential, players generally start with a starship, too, although the terms of ownership likely include a lease-to-buy option where the crew are constantly on the lookout for jobs to keep up payments. There are plenty of ready-made examples, including the Nostromo and Sulaco, or your players can make their own from scratch. There are extensive options for modifying or upgrading your ship, and ship-to-ship combat is generally streamlined and includes all players in some manner.
Combat between characters and NPCs is likewise straightforward, and quite brutal: Hit points are based off the Strength attribute, and humans can't raise that above 5 (synthetics have higher limits), so it doesn't take much damage to bring a player down to 0 health, where they become "Broken". While Broken any further damage calls for rolls on Critical Injury tables, so while it's easy to become Broken, it's considerably harder to die. I prefer this method myself, as a long-surviving character with many scars is a lot more compelling than making up a new character every couple of weeks.
Finally, the Aliens themselves are treated with a good deal of respect and operate very well within the mechanics. There are various types drawing from all the films, from facehugger to Queen to the colossal crusher xenomorph from the otherwise rather dull Colonial Marines video game. The youngest stages are quite squishy, but every xenomorph is fast, strong, stealthy and hideously dangerous. They have a table of signature attacks, so not even the GM knows what they'll do all the time. And if you do manage to reduce one to 0 health (and avoid the resulting acid splashes), they have randomised deaths which could take an unwary or unlucky player with them. For players roleplaying a group of civilian traders, one xenomorph stalking them is probably enough to keep them busy for multiple sessions. Combat heavy games, where the players are all hardened soldiers, could make short work of a few xenomorphs at a time, but ammo runs out, and without regular breaks to relieve stress their luck will run out.
There's enough material in the core book to run a campaign where the players never even see a xenomorph. Space travel, corporate treachery and frontier life are hostile enough, but they make for excellent antagonists, used sparingly. There are even a few other nonhuman creatures thrown in, most likely from the comics universe. There's a planned expansion in the works that deals with the US Colonial Marines in greater detail. The available adventures and maps are of excellent quality. The artwork throughout the book is sublime (the black makes for very poor character sheet prints though, you should find the printer-friendly version online!)
I'd have preferred an expanded list of skills ("Comtech" includes everything from bioligy to computer networking, which is a bit strange), and more information on the Union of Progressive Peoples (Space Russia analogue) and their various star systems would have been awesome, but all in all Alien is a simple, clever RPG jam-packed with atmosphere. Absolutely worth the price.