A story of this quality hurts itself enough that spoilers probably wouldn't affect your experience that much but I'll warn you that they're present in this review anyway.
(single player, veteran difficulty)
One has to wonder why almost every remotely intriguing character in Killzone dies or is forgotten but the monstrosity that is Rico Velasquez is allowed to to be a main character in all three games? Yes as you probably have already gathered Killzone 3 suffers from weak characters and dialogues once again, but to be fair Guerrilla obviously tried to shed, or at least alleviate these constraints this time around. The plot is is more interesting and intricate than 2, and the implementation/explanation of the setting is much better than in the past, but once you consider the stories of past entries much better is still sub par. Killzone consistently has some of the best opening scenes I've ever seen but its presentation is tragically not translated to the main game, even though the plot on paper is pretty good and the setting is astoundingly unique and ripe for compelling tales. Once again nearly all bearable major characters are on the Helghan side of the conflict, leaving most of the ISA with cliche ridden caricatures. Rico is now slightly more tolerable and Sev the opposite, Jammer barely registers as a character, Kowalski dies not long after his entry, Captain Narville is okay, and their are no other "good guys" that are really even named. Every bit of ISA dialogue sounds familiar, and my theory for this is that the writes yanked conversations from every piece of action media ever made then smashed it together to create the ISA's script. As I said the Helghast are still an incredibly intriguing race, and while none of it's senate measure's up to Scolar Visari their rants are quite entertaining if not suffering a little from the same banality as the rest of the plot. Though lacking, the plot's pacing is perfect. As I said in my Killzone 2 review, the intense combat tells its on story through the emotions it invokes and the yelling of the troops.
Fortunately, Killzone 3's gameplay and effects more than compensates for its impaired plot. Killzone is one of the most gorgeou.s series out there period, whether you're listening to the hackneyed words of rico; perfectly corresponding music; or the chaotic sounds of war everything you hear is top-notch, and every gun shot or melee feels outstanding. Tweaks to the gameplay like the ability to slide to cover, destroy more of the environment, carry three weapons, companion revives, and so on make the experience less nerve racking and difficult but ultimately make it all more enjoyable. Vehicle sections are fun and action packed, and new weapons like the WASP or jetpack add news and interesting ways to eliminate your foes. Though Killzone 2 was entirely in an urban setting 3 takes you to a multitude of drastically different locations with unique obstacles that will require you to use jetpacks, stealth, and more to pass them; none of the levels particular complications feel tacked on and enjoyably add to the games excitement and diversity. The former urban setting added to the action and tension due to its close quarters combat, but 3's level diversity (some of which is close quarters) keeps the fighting thrilling. The Helghast is still the most intelligent and blood thirsty AI out there and friendly ISA troopers are surprisingly astute, and even though the battles are on a smaller scale than 2 both perform impressively and further contribute to the general feeling of war.
Though I spent half the review expressing my displeasure with the presentation of the plot Killzone 3 is a superb game and very worthy sequel, and it's just that I'm so incredibly disappointed that a fantastic setting such as this isn't being adequately represented in the story that I dragged the subject out so long. 3 retains everything that made 2 one the best FPS's and games in general ever and adds to it's formula in new and exciting ways, and if Guerrilla manages to make future Killzone's story as good as their gameplay gamers are going to be in for one hell of a treat.