Regarding some minor technical flaws, this game will be remembered as the next-step in FPS games.
Besides the technical stuff, the single-player campaign is great, although a little short (leaving an opening for sequels). Great voice-acting (stands out when Aztec prays in spanish for his life in the early-game) and ambient sound, smooth gameplay, nice enemy IA, several tactical option for complete an objective and the vast inventory of weapons, weapon-customization items and vehicles adds a lot.
(Warning: some spoilers)
The only set-back was some minor flaws, pretty countournable. I had some trouble in the Courier stage with the collision detection system of the engine. Right after the nuclear attack to the island and the alien's counter-attack, the floor of the Almirant's cabin did not hold any collision properties, and the player's and almirant's bounding-boxes just fall to the middle of the ship in a polygon-void area. Weird, but resolved with a game "reboot". I still haven't played the game with the recent released update patch, so I hope this is fixed.
I also didn't have the opportunity to play the multiplayer feature, but, from far as I'd seen, the Power Struggle mode sounds like a LOT of fun.
Resuming, this game aimed to be in the history of the FPS genre, as Half-Life, Wolfenstein 3D or Doom, and one can say that it succeeded.