CE esque everything (mostly)!!
-I want enemies to be susceptible to manipulation like in CE and H2. In CE, I could shoot my gun from behind a wall and alter AI behavior. I could kill off a bunch of Covies leaving only one, go into hiding, and come back up to find him patrolling.
-I want AI to be responsive but also show a variety of reactions. I loved how Grunts would jump around trying to get the grenade off their face and how Elites would run around in circles when stuck. Now look. You stick them, they just run forward. You get needler shards in them, they don’t do anything. It’s so vulgar and unlifelike!
-I want allies to stop driving off with my vehicles and to stay in the freaking hog (only once in CE did they get out of the hog on their own and that was the overturned hog on AotCR).
-I want powerful weapons and big melee range so I can feel like a boss. Post CE, meleeing an infection form is incredibly difficult. Post CE, if I try to use a weapon other than the pistol, BR, DMR, sniper, rocket launcher, etc., I lose my shields unless I’m firing from adequate cover. I want to use my favorite weapon, the plasma rifle, yet I can’t do it because of how fast the projectile speed of most guns are. Post CE, lunge and autoaim are unacceptable.
-I want to benefit from difficulty increase (in CE, player received a shield recharge rate increase. In Reach, projectile speed got increased but it didn’t help me at all on Legendary).
-I want player equal enemies that seem like player equivalents. H3 Brutes were pathetic while Reach Elites had way too many advantages (I liked the faster grenade throwing though since AI tend to stick each other more when they do that slow grenade toss). Both made all sort of bad mistakes, such as when losing their shield, they berserked (Tough Luck induced this state in H3 Brutes but I’m not sure about Reach Elites). The Brutes with brute shots would fire at the player, even if the ground was right in front of them, losing their power armor.
-shield bleedthrough for shots. No shield bleedthrough in addition to Bloom severely limited weapons in Reach
-I want bumpy vehicle physics. CE’s hog was more easier to fit into closer spaces because of how it bounced against walls. It was also more easier to park… it also didn’t flip that much and I liked how marines on the turret would do that yee haw animation. 
-I want no vehicle health. That is extremely annoying, especially when you have EMP plasma pistol overcharge spammers.
-No more vehicle durability sacrificed for power. I hated that. The Reach Banshee, the Reach Wraith, etc. Also, give better traction and vehicle control. The H3 Wraith and Banshee were disappointments. Same thing with the H3 Ghosts. The Ghost had some difficulty climbing up slanted cliffs if it didn’t have a speed boost. With the Wraith, I had to fire a heck lot of mortars to get myself back on the ground. I liked how in H2, I could squeeze the thing through the gap in the control room.
CE: Immersive, genuine enemies
H2: Somewhat immersive, somewhat robot enemies
H3: Breaks immersion, robot enemies
Reach: Breaks immersion, robot enemies