They're noticeably different. Not so much as Halo CE to Halo 2, but that's the way of gaming. Smaller leaps. --- You can't make an omelette without crushing dozens of eggs beneath your steel boot and then publicly disemboweling the chickens that laid them as a warning.
I never thought halo 3 looked impressive at all despite 4 player co op. it looks pretty damn solid in 4 players the lighting and stuff doesnt get shafted like reach and it runs more stable (with very little in terms of frame drops).
i remember when halo2 came out it looked amazing. i was just wowed at the graphics. Halo3 i remember when it came out and i was like WTF this barely looks better then halo2. Halo 2 used the Xboxs hardware really well halo3 not to much. --- ErrorSupply 3-D DS -OMG! It's the ultimate anti-pirate tech O:.