What Treyarch did right/well:
Post Game Support - Their post game support was remarkable. Releasing patches regularly, fixing exploits, tweaking of guns and also the addition of the playlists. Introducing the competitive playlist was a great idea, although it wasn't populated that well, allowing a subsect of the gaming community to play with one another without having to log onto a gaming website is great. Also the introduction of the Express playlist was also very smart and I do thank the devs for what they did.
In Game Scoreboard/Score Per Minute - The in game scoreboard was an excellent addition to the game and I praise you guys highly for it. Allowing players to see their own and others 'work' for their team is a great idea. I really do hope to see the return of the scoreboard in the next Treyarch game. Score per minute was fantastic and is used as a way for a player to challenge themselves during the later stages of the game's life cycle and again I commend the devs highly for this.
Create-A-Class - The create a class user interface was excellent a big step up from previous titles. I like being able to change camo without having to select the gun category, the gun, the attachment and then finally the camo. Also I like the Equipment - Lethal - Tactical slots. I think that grenades should be replenishable with scavenger and so to tactical grenades (except if a perk like MW3's hardline pro is introduced because the ability to continually throw stuns and gain killstreaks is extremely unbalanced).
Community Feedback - I loved being able to ask questions and be notified of patches/updates or possible server downtime via twitter/facebook. I love how the whole company listens and works well with the community.
MAP PACKS!!! - I loved the constant DLC. A map pack released every 2 months (after the first 3 months of the games release) was fantastic! It always kept the game fresh and enjoyable and I do commend you on that.
Spawn system - Call of Duty has small maps (compared to some other shooters) and with the amount of players on the maps spawns can be frantic and the occasional-rare unlucky spawn is always going to happen. I love the spawn system in domination (the game mode I play the most). If you had A & B Flag you would spawn somewhere in between the two, for example on summit you would spawn in/near the generator room on the catwalk side of the map, or up in the top control room whereas in MW2 (for example) if you had control of C & B Flags and you were killed as an enemy tried to capture B flag you would respawn in the green room (underneath the helipad) and would be able to kill them easily. I like that if I'm trying to cap B I can kill a couple of enemies near the B Flag and now that they shouldn't be able to respawn and kill me from behind.
CoD Points - I'm not too certain how I feel about MW3's levelling up a weapon's feature and I am still unsure which is better gradually unlocking attachments or being able to buy them instantly. But I do commend you for trying something new, personally I liked being able to buy camo's at any time (except for gold camo) but I did also like the challenge of earning my red tiger camo. If you take either of these paths, that will be fine by many but take into consideration that people do like to be rewarded for playing the game as unnecessary as it its I prestiged to 14th prestige just so I could get gold guns.
Theatre - I loved the introduction of theatre mode and hope that it returns in the next game. I would appreciate the option of turning theatre mode off in the next game though. I'm uncertain if turning theatre mode off will impact the connection during a match, though it has been rumored too.
Boosters - THANKYOU SO MUCH FOR REMOVING TACTICAL INSERTIONS FROM FREE-FOR-ALL!!! I love that I can play a game of FFA without needing to worry about boosters who are trying to get Attack Dogs. This is also an arguement for keeping the CoD points system though as headshots aren't required to earn the camo's. I also like the report player function.
Combat Record - I loved the introduction of the combat record and loved how easy it was to compare stats with friends. I really wish that this makes a return but I would also wish for an ability to make it private, though it will come at a cost where you cannot see others combat records. The only reason I wish to be able to hide my combat record is because when we (as a party) are searching for a game players tend to leave after looking at our combat records'.
Removal of annoying/overpowered perks from previous games - thankyou for removing Dangerclose, weakening Noob Tubes, Deathstreaks, Commando and One Man Army (I'm still uncertain about the removal of stopping power as I do not wish for ghost to be overpowered).
Wager Matches - I LOVED wager matches and were always fun to play. If the CoD point system is not returning I wish to have these game modes in a private match or be in a playlist, which is explained below.
Snipers - I am not a sniper but I do enjoy playing with the sniper occasionly. Please do not allow fast/faster aiming down sights with a sniper rifle. If this is allowed in the hands of some players a sniper rifle is a shot gun at close range. But I do not believe the sniper 'nerf' was a great idea either. The sniping should be similar to that in CoD 4 and CoD: WaW.
MOST IMPORTANTLY: (Not really)
FIRING RANGE!!! : firing range is the best map in Call of Duty history. It is small enough to encourage aggressive play but large enough to not be extremely hectic with several choke points. Please, Please bring back Firing Range on DLC or remake it or do something. PLEASE!!! I would pay $15 just for the one map.
How they can improve:
Weapon balancing - The weapons weren't balanced too well. It is understandable to have several strong weapons which are better than others, but there should never be one gun that is always better than the others in its class. Weapon balancing is EXTREMELY important almost as much so as perk balance and a high volume of effort and thought should be put into it.
Perk balancing (emphasis on GHOST) - Many of the hardcore CoD fans believed that Ghost was 'extremely ALL CAPS overpowered' but it really isn't. Compared to the other perks in its tier it was perhaps the most powerful but not 'extremely ALL CAPS overpowered'. I do not wish for the perk to be removed as a whole as it is a perk hiding you from killstreaks is needed and people need to remember that the game is a 'First Person Shooter' and not a 'Use My Killstreak To Destroy n00bs'. Although balancing the perks is needed. NOTE: there should not be a perk counter to a 'counter UAV' or 'counter spy plane' and an EMP and some of the counters to ghost/assassin need to be in place. Also the blackbird/advanced uav should show ghost/assassin users on the minimap and should not be shot down.
Cool Stuff from MW3 - Introduce the prestige shop, support/specialist/assault strike packages, private game modes etc.
Game Modes - Be open to the introduction of new game modes and please. Either you can 'hide/lock' the game modes on the disc or allow it in the coding to introduce new game modes in updates. Repeatedly playing fun things eventually makes it less fun so being able to introduce new game modes will be awesome. There are a lot of players who care about their statistics, introduce a playlist were the games do not count to statistics but only with non core game mades e.g. sharpshooter, infection etc. This allows players to play without the constant worry of having a 2.5 kill death ratio all game and when players do not care about statistics they will rush and will make the game more fast paced.
Maps - Call of Duty is recognised and is popular for its fast paced action. Maps need to be developed which can fit these criteria. The majority of the maps need to be Small - Medium Sized (As mentioned earlier firing range is the best map in Call of Duty History). I believe that maps need to be altered for different game modes, like how areas were closed off in wager matches. For example Array Free-For All would be split in half to encourage aggressive play styles. I am not saying that all maps made should be small because there are thousands of ground war players who need the larger maps but being able to play those maps on smaller scales when less players are involved will be amazing. AND PLEASE NO LARGE SNOW MAPS IT MAKES GHILLIE SUIT SNIPERS TO HARD TO FIND.
Keep deathstreaks away - deathstreaks were extremely annoying in MW2 and with MW3 they are almost as frustrating. That is not to say all deathstreaks are bad but a player should not be rewarded for dying 5 times in a row. If possible keep deathstreaks away! If deathstreaks have to be introduced bring back copycat, juiced, martydom and hollow points are great deathstreaks.
SECOND CHANCE - Please do not bring back second chance, it is extremely frustrating and annoying but if it has to come back reward the player who puts the enemy into second chance and not the team mate who kills him.
Sound Engine - Please make improvements to the sound engine. I know that allowing a player to hear an enemy from a mile away is over powered but sound is an important asset to any player and adds to the overall experience of playing the game.
This took me a while to type and brain storm ideas so please share and try to get Vahn (Vonderhaar) to read it.