First off it's Halo
Campaign -
Pros - Superb voice acting, alongside amazing animations and visuals, really submerge the player into the story. In my opinion the best story telling to date for the series, they give you enough info to keep you in the loop, but always wanting to know what happens next.
Cons - The campaign was really short unfortunately, and fairly easy. It can be beaten in an afternoon if you have a decent amount of time (4-8 hours depending on difficulty) I was able to complete it in 8 hours on legendary, and for the hardest mode available, it still seemed easy compared to Halo 3's legendary.
Multiplayer -
Pros - The announcer, I'm convinced that the announcer adds a lot to the multiplayer of any game, and this is still one of my favorites, but with now updated announcements. Lots of customization, everything is customizable from head to toe, and have lots of options. Load-outs were done really well and none of the perks give a huge advantage to higher players. Ordnance drops (aka score streaks) is a nice change of pace for the game as well. Giving players a choice between a power up (speed boast, damage boast, over shield) and 2 power weapons / grenades is a great addition to a stagnant MP. Also the new weapon additions sound amazing and are alot of fun to use as well, my personal 2 favorites would be the SAW and Binary Rifle. Lastly the assassinations, one of the most enjoyable things about this game is the animations when performing an assassination on a player.
Cons - The DMR and Boltshot seemed to be overpowered for starting weapons. DMR is a 4/5 shot kill if you time your shots correctly, but the bloom has been significantly reduced so it really doesn't take that much skill anymore, and the Boltshot is a 1 shot kill should you be short - mid range. Some of the launch maps aren't used in the multiplayer playlists which is kind of disappointing that they don't use all their maps and pump out DLC. Matchmaking is completely randomized at the time of writing this, matchmaking does not match you up against similarly skilled players so one game you might go 43 and 7 k/d and the next you might go 5 and 20. Lastly, they frequently remove/ update their MP playlist, yes this wouldn't usually be a con if they left in all the play modes instead of cycling them in and out.
Overall -
I really enjoyed Halo 4 for the few months I had the game, with a intriguing story and addictive multiplayer, this is a welcomed addition to a stagnant series, be warned though, as with all halo's comes rage quits and at times questionable deaths/ bullet damage.