Dibbz said:
KZ2 = Polished because it was in development for a fuck load longer than KZ3 and Sony didn't want to rush it out.
Or because they made an entirely new engine on an entirely new system (which is commonly known as the most frustrating system to program on).
Because they made entirely new assets.
And, although uncertain, because they also developed Killzone Liberation simultaneously.
Looking at Killzone 2, it's quite amazing what they managed to achieve in the span of time.
With Killzone 3, they already had the engine, they already had like 50% of the models and textures. They already had a bunch of sound effects and (enemy) voices. Not to mention Guerrilla Games has expanded quite well after Killzone 2's release.
There is absolutely no reason for Killzone 3's horrible,
horrible state. Jesus Christ, the intro movie alone just shoved 'rushjob' right into your face. From the goddamn start of the game it tells you it's going to be a cut corner ride.
The only explanation I can think of is that Guerrilla Games put half its staff on a different project. But did they? The credits felt like twice the entirety of KZ2's.
If Killzone 3 had the time KZ2 was given it the SP would have smashed KZ2 out of the water. In the end the SP was only just better.
I see no evidence of this being a possible in an alternate timeline. The only thing I liked about KZ3's story is how it showed more about the higher-ups of Helghast. Besides that, the only way KZ3's SP could've blown its predecessor's out of the water is if they wrote an entirely different story.