I tried Halo 3 yesterday to see how things felt compared to Reach, and overall 3 had just a better feel, let me explain why:
Grenade release - In Halo 3 the grenades were small and came out of your hand a split second after you pressed the button (not to mention they were balanced). In Reach they are huge, overpowered, and take longer to release, and I find it a lot harder to stick people.
Sniper rifle - In 3 it didn’t take up half your screen and the bullets registered more. I hear in Reach people have a larger hit box for the head, but I find myself never getting a headshot, while in Halo 3 I snipe like a pro, no scopes left and right.
Movement - I’d say keep equipment in Halo 4 but leave sprint (similar to CoD). Halo 3’s movement was a lot more… manuverable and smooth, in Reach it’s clunky and slow.
Forge colors - Halo 3 things were more appealing in forge, and while Reach’s forge is good, you only have grey and blue, and not to mention you only really have two maps to forge on.
DMR - I know this one is said a lot but there’s no better feeling in Halo than getting a 4 shot with a BR. Also, bloom ruins the DMR, but you’ve already heard this so I won’t explain.
Anyway, those were the subtile things in Halo 3 that I noticed were lacking in Reach and I’d like to see in Halo 4.