Absolutly phenomenal.
The game features systems that have been featured in other first-person shooters, including Metroid Prime, Tom Clancy's Rainbow Six, and Halo. The Heads-Up Display (HUD) in the game has a similar feel to that in Metroid Prime. The squad-based order system is similar to the Rainbow Six games, where certain positions are tied to an action. Pressing the order key will tell one of the squad to move to that position and do a predefined action, such as providing sniper or anti-armor fire. There are also orders that govern the entire squad, such as Search and Destroy, Hold Position, Form Up, and Recall. The player can only carry 2-3 guns during the game, though the main gun can acquire attachments to suit different needs, such as: Sniper fire, RPG Anti-Armor, and the standard ion blaster. When playing in campaign, you do not die, you are simply downed, and need to be healed by one of your squadmates.
Despite a rather short campign, it is the best campaign I have played, and probably will play for a long time. The game just throws wave after wave of enemies at you. It is actually quite a hard game, the hardest misson being "A bridge too far". The multiply is good, but they should have focused more on the maps (and try not to copy them from Halo). The weapons are different from your standard shooter game weapons. You have a 3 in 1 rifle/sniper/RPG, a massive chaingun, a bowcaster, a beam weapon, a concussion rifle and a crappy repeater gun. There needs to be deeper squad command though, as all you can really do it get them to take up one of four offencive positions and then the basic squad commands.
The graphics are great, nice and crisp and pay fine attention to detail. The games theme "Clones" is done by Ash, not exactly a good band, but it is a good song.
The Good: Absolutly gob-smacking single player, great graphics, good multiplayer, challenging
The Bad: Short campagin, the damn ending (it is a good ending, but it sucks what happens), and the worst of all, it isn't backwards compatible
So in conclusion, if you have ever wanted to enjoy a game at all, please, PLEASE get this.