Campaign: Words really cant express what I think of the campaign, but I will try. Exciting, full of emotion and full of intense challenges. One out of many of the best Halo campaigns ever.
Multiplayer: The multiplayer has a lot to it so I will try to break it down. Now my overall view of the multiplayer is that is it what Halo is all about. The intense moments, thinking on your feet, working as a team, communication, and most importantly, it is very competitive. I think 343i really did an amazing job on the multiplayer. With that said there is still some things I think could be improved.
-Ranking: The ranking system is great with all the stuff you unlock for your Spartan, emblems, etc; but my biggest concern is that we level up too fast. Never in any Halo game have we leveled up this quickly.
-Maps: The maps are very different in their own way and some I like and some I hate, which is natural for me. The BTB maps I don't really care for except for two; Exile & Ragnorok. The map Complex in Infinity Slayer I feel should be a BTB map because it is to big for 4v4 in my opinion at least. So I am hoping that the DLC offer some great maps.
Map voting is executed well with not being able change your vote after selecting one; but I would like the "None of These" option in-case I don't want to play on the maps were given to choose from. Also there needs to be more variety, maybe even have us play on the forge maps, just have maps pre-built by 343i.
-Weapons: The weapon choices are very unique, but also we have some familiar guns returning from the Halo universe, especially from Halo 3. That makes me happy. The weapons I feel are pretty balanced, but I always wonder how a BR can get out beat by a DMR. Now I do like the power weapons being Ordnance drop, but I would like a game mode where they are placed on the map and have no Ordnance drops.
-Grenades: Grenades seem to be very weak compared to the other Halo games. Reason I say this is because I have stuck a ghost with 1 grenade in previous Halo games and it explodes. You do that in Halo 4 and it doesn't destroy it in one blow, which is disappointing. Another example is when I throw a frag or plasma grenade at someone and they are right on it and it doesn't kill them. Just lights them up like a Christmas tree, which realistically they should die. Also the blast radius of the grenades needs to be slightly increased.
-Vehicles: The vehicles are freaking awesome with the way they look, sound and handle. The only issue I have is the warthog gun turret. I cannot tell whether or not I am on the person because the reticle is so small.
-Armor Abilities: The armor abilities are great except thruster pack.
Thruster pack seems like it was made to replace evade, but it only moves you like 1-5 inches away and lasts a split second. Its a useless ability.
-Game Modes: This is disappointing to see that there aren't a lot of game modes at launch, but I am assuming they are going to give us more in an update =] *crosses fingers and hopes >.<*
That is all I can think of right now, but if I come up with more stuff I will post it :)