Okay.
Im an avid Halo fan and also a fan of most shooters out there, as most of you know, we all wish some aspects of some games had been incorporated into others or that some things should just have never been added into some games. Now im looking forward to Halo 4 as much as everyone else but im really doubtful of what to expect, Halo 3 Delivered tremendously, no doubting it. ODST… 
Reach was also very awesome and I still play it now. But there are certain things in Reach that I would love to see incorporated into Halo 4 and also some things taken out.
Im going to start with some things that I really think need to be carried across:
Ranks:
The ranking system in Halo Reach, for me, is a lot better than the one in Halo 3. I prefer a credit system which allows players to eventually level up their character over a period of time. I understand that the Ranking system was updated in Halo 3 aftwer a while so that individual play lists had ranks but at that tie I wasnt playing it as much so I cant really comment.
I think that the idea of Ranked and social playlists would be better if the ranking system was to be taken back to Halo 3, the social playlist would only give you credits where as the ranked playlist would give you a number ranking and also credits, this offers players the choice to play competitively or just for fun.
Playlists:
In terms of playlists on Halo Reach, I think they did a great job, not excellent but great. I hope that in Halo 4 there is more specificity homed in so that players are not forced to play things which are voted by others players that they did not initially want to play.
I also wish to see that the variation of gametypes available to players is increased, I know there is at the moement a lot but I personally would love to see more custom game modes put into the matchmaking list, or why not even create a whole new search list specifically for Custom Games? I am pretty sure that I am not alone in the fact that Custom Games is one of my favousrite things to do in Halo, other than Forge 
There could be a search section like how ‘Gears of War’ had it, players could host games which they could then advertise on a server list, which im guessing could be filtered to, everyone, or regional, or a specific area so that the list of games wouldnt overflow. You would obviously also be able to filter your search to say infection or Slayer or any other game mode you want to play.
Armour:
More armour please, that is all.
Forge:
Obviously Forge is loved by all and im guessing it will be in Halo 4. Maybe give us more maps like ForgeWorld, this would be awesome. Maybe 2 or 3 like it, not all the same as forge world, it can be a little tedious making maps in such a bright environment, maybe some city based maps so we dont have to make all our buildings. On that note… add more variation into what we can add please, Halo 3 had loads of cool little things around to add decoration, it lacked proper building blocks, but it had decoration. Halo Reach added the building blocks but lacked on decoration, the balance needs to be found so that all maps dont look the same.
All maps Should be have the same properties as forge worlds, I mean that objects should be able to be ‘mushed’ into things as they are on Forgeworld rather than just spazzing out when tried touching.
Things that need to be considered and improved on:
Abilities:
Okay, so Halo 3 was amazing, lets all agree, but it could have done with sprint…
Halo Reach- BANG… Sprint. Oh, and heres jetpack, shi… Armour lock, invisibility dodge and decoy? Hmm… we really only needed sprint to be honest, but okay, cheers for the rest. NO… We really only need sprint, please take out the others and dont add anymore in! Maybe Jetpack can be used in custom games as it can be fun but the others just create too much BS in PVP. Please take them out.
Armour:
It was poor, lets be honest. Make it look cooler, when I unlock a helmet I want to like the helmet, not hate it. Halo Reach Helmets were pretty bad, not all of them, but like… hmmm… 80% were S**T.
Bring back the Katana Please.
Achievements:
The Achioevements in Reach were not too bad, fairly easy to get them but there wasnt enough of them. Halo 3 had a nice balance I think, some achievements were overly hard, 2 kills with a spartan laser in matchmaking… fairly hard to be honest lol. But it had a lot of them and that was good. I think it is cool to have a decent amount of achievements, keeps the game fresh and it adds more things to do.
Weapons:
Obviousley Halo 3 is after Halo Reach in terms of the timeline, so the weapons in Halo 4 will be different to Reach. Im hoiping to see the BR come back, dont change it from Halo 3, just add some saucy textures and make it look cool as S**T!
I think that seeing as now the story is in your hands you havge the opportunbity to maybe add in some new weapons, I havnt read the books so if the game follows the story of the books I am unaware of this and appologise, if not…
I think we need a new AR, the AR at the minute is, to be honest, pretty -Yoink-. Its only use is to be used at close range being sprayed as you charge into your opponent spamming melee… yeh, I do that. New AR please.
Other than all the points that I have put abvove ;/
I think you will do a great job, look forward to Halo 4 and I will be buying at midnight release, dont let me down… no seriously, please dont.