The only complaint I can level against the game is a lack of Brian Cox and his awesome speeches.
This is going to be a short review as I could easily copy and paste - with some minor tweaking - what I say about the graphics and use that to explain why the sound is so good and whatever else about the game. Everything is just so sturdy and so good that the entire package comes together to form something so effortlessly enjoyable that I cannot wait to pick up the third Killzone and delve back into the Helghast world. From the detailed and moody environments to the superb animation and sound, the clever AI and varied gameplay Killzone 2 triumphs as a shooter. Going from gritty, cramp and slow urban combat to a windy desert is a visual and tactical treat. The cover system is also really well done as I rarely got stuck on objects I didn't want to be stuck on, for an FPS with a cover system that's saying something.
The multiplayer is also really well done and that's coming from someone who really doesn't play online all that much. Even after two and a half years I can find a full game (admittedly it's usually the only game to play) and play for an hour and leave satisfied. The nice touch is that the objectives alternate between a list of choices. Find a territory and hold it against the enemy, defend a point or assault it, assassinate a player or defend your own, retrieve an important object and escort it to the enemy base and good ol' body count which is team slayer. Tried and true staples but it's the alternating nature of the matches that makes it enjoyable, losing a round of body count isn't a big deal when assassination is up next and your target is close by.
The only complaint is the story that takes an absolute backseat to everything else and that's a shame as this world is begging for a good tale. Conflicting ideologies and justification of invasion and conquest would make for an awesome story but that just isn't here. What we get is a ho-hum yarn with awful characters as your teammates. The ending will have you hating Rico with a passion and questioning why anyone would call him 'comrade'.
Killzone 2 really is the most solid shooter I've ever played. While other games will shine in one area and fall in another Killzone 2 stays relatively awesome in every category possible.