Area-51 is an action packed twist on the sci-fi genre. Indeed the "truth is out there" and it is surprising.
I guess one could describe Area-51 as a horror-survival FPS. That said there are interesting "asides" and nods to the alien's visiting earth genre as well as an expose about the alleged NASA landing on the moon! It is really in the exploration of the deeper levels of the Area-51 complex that the story really gets cracking and becomes more sci-fi than horror focused. Don't be mislead, these are not the friendly aliens of Steven Spielberg. The story is smoothly advanced by cut-scenes and Duchovny's voice overs during the loading screens.
Area 51 has a storyline that runs for 19 "chapters" and the narrative becomes more convoluted and indeed the game itself becomes increasingly harder as you progress. Alas there are no quick saves and you may, from about chapter 12, find that you will need to replay segments of the level a number of times as the game does get more difficult, although there are health packs in the form of injections scattered around each level. From chapter 17 the game became quite challenging as extended "boss fights" (which I loathe in any FPS) came to the fore.
Overall gameplay was typical shooter with the protagonist carrying multiple weapons. The story provides a variety of enemies which range from lumbering mutants to alien drones however combat can be quite intense and enemy AI is reasonably good in most cases. Ethan Cole, as the game progresses, can also use some alien technology and the "mutagen" virus to enhance his capabilities. Alas there were, for me, too many boss fights that ruin the pacing as these often needed multiple replays to work out how to destroy them in order to progress.
The game is reasonably graphics intensive and a few tweaks on your graphics card GUI may be required before it runs smoothly. One cannot really fault the graphics and sound work on this game.
OVERALL: While it took me a while to get into it I ended up really enjoying Area-51, although some may find the game somewhat linear and scripted.