I am worried about several things:
-Beta- I hear rumours that H4 is going to be one of the release games for the next Xbox, this would make a lot of sense as it definitely seems 343 are on a really strict time schedule. A beta allows players to give the developer feedback on how the game plays and allows a lot of bugs to be found before the game ships. It also means players can try the online game before buying it.
So 343 why are you not releasing a beta? Are you cutting corners to save time and/or Are you worried people won’t like it?
-Armour Abilities-
It appears at least some of the AA’s are going to make a return in H4, in the videos released thus far Sprint seems to be default in all playlists and perhaps some sort of thruster pack. I dearly hope that hologram/camo/armour lock will not be returning as they do not promote more skillful play.
Personally I would prefer the game with no default AA’s but at the very most I would want Sprint and some sort of jetpack, with the jetpack being either pick up only or specific to certain maps.
-Perks- 343 are planning to allow players to change there Spartans in ways that aren’t purely cosmetic and they have directly compared what they are planning to introduce to the COD perk system. Obviously I doubt they will be as powerful as some of the COD perks in certain situations.
I just don’t see how perks will fit into the game because Halo has always been a game where in the game everyone is on a equal footing in a game, and the ability to select different equipment/perks doesn’t promote an equal battlefield. I think if they moved the credit system to Call of Duty that would be a much better move.
-Halo CEA- They re-textured just 6 of Halo CE’s maps and then used the halo reach engine to play the multiplayer online. Even so I liked how CEA played but I couldn’t help but feel 343 could have done a lot more on the multiplayer and it felt nothing like Halo CE.
I really hope 343 actually change the engine considerably from halo reach so it is more fast paced and rewards more skillful play.
Summary of what I want to see in H4
-Trueskill ranking system (Halo 2/Halo 3)
-Faster Movement/Higher Jump
-3/4 Shot kill with BR/Pistol
-10+ maps on release hopefully a couple of remakes
-No Hologram/Armour Lock/Camo Armour Abilities whatsoever
-Pickupable Camo/Overshield/jetpack?/sprint?
-No non cosmetic equipment/ability choices
-Improved Challenges/Commendations/Credit system
-Zero Bloom or heavily nerfed bloom
I still have hope in 343 Industries for Halo 4 but I am very skeptical about whether it will meet at least some of my hopes. 
Thoughts? And Are you worried too?