To help people compare, here's two videos, both HD from gametrailers, both demoing the latest build of each game.
Gears 2.
Killzone 2.
Killzone 2 looks better to me. Here's my reasoning:
-- Gears 2's framerate is all over the place. Whenever something dramatic or cool happens, it drops painfully. Whenever I watch this gameplay video, I tend to feel slightly nausious in places because of this.
-- Does no one else notice the way the dead bodies in Gears 2 disapear whilst on screen (they simply pop out of existance)? I haven't seen anything like that in Killzone 2.
-- Check out the graphics on the guns in Killzone 2. Looks nothing short of amazing.
-- Lighting is much better in Killzone 2. Look at the way it shines through the windows.
-- I notice more 'active enemies' in Killzone 2. By 'active enemies', I means ones you actually fight. The horde of Locust you see at the end of the Gears 2 video strike me as rather unimpressive: you see a bunch of them from a distance (and so are presumably at a lower res than normal enemies), and they only seem to have a single AI directive (run forwards, no matter what). In the above video, you never see more than two 'active' enemies on the screen at any given time.
-- Animations, especially the death animations, are far more impressive in Killzone 2. The Locust are either cut apart in a predetermined, canned manner, or else simply slump to the floor when shot. The mixture of rag doll, canned animation and environmental reaction in Killzone 2's death animation are far more impressive (notice, too, how blood leaks out of the Helghast after they've died).
-- The explosions look more impressive in Killzone 2. Explosions are important to me.
In favour of Gears 2, I have:
-- A larger draw distance. I really love this, and I think it's the game's main advantage over Killzone 2. It gives the level above a truly epic feel. In all the videos I've watched of Killzone 2, I haven't seen it show off such an impressive draw distance.
-- Killzone 2 has a fair number of low-res textures. Check out the textures on the mounted gun at the begining of the video, for example. There's no textures quite so unpolished in Gears 2.
-- The character models in Gears 2 feel slightly more 'solid' than the Killzone 2 ones.
Both games look awesome, and both have their fair share of problems. At the moment, Killzone 2 really does look noticeably better than Gears 2, but with plenty of time left to polish each game, I'll hold off making an absolutely final decision until both games have been released.
