Halo 4 has had an overwhelmingly negative reaction from the hardcore community due to its adoption of CoD systems in the multiplayer such as loadouts, perks, instant respawn, and personal ordnance (aka point streak rewards) because they add random and unpredictable elements to the sandbox and cause major balance issues.
There are tons of other issues and bugs and glitches as well. An example of this is that ingame file browser, which allows us to view screenshots, films, custom maps and gametypes, has not worked since launch and there is no ETA on when it will become more than an error message. Bungie had hosted an online version of this on their website during their Halo 3 and Reach days, and you could even queue up files to download automatically the next time you started the game. This service is now gone as well.
Halo 4 is also the first Halo game with matchmaking that lacks any kind of ranking that is determined by skill - there's no arena or league playlist or anything like that, just keep playing and getting XP.
There was also recently an issue where Microsoft accidentally made the first map pack free for everyone who played in the first two weeks the game was out, and they had to revoke it via a title update. Title updates reset the system that uses game history to determine host, so laggy matches galore for many of us.
The campaign has become more focused on linear firefights and corridors rather than open areas and exploration, "because we wanted to do what Call of Duty does," according to a developer interview. The cutscenes have really bad audio compression.
Spartan Ops replaced Firefight, which was Halo's take on a horde mode. Firefight was highly customizable, Spartan Ops sacrifices that to tell a linear story. We were promised brand new environments, of which we got a few, but the majority of chapters take place in areas recycled from campaign and multiplayer, most of which are repeated several times. The mission design is almost always to kill enemies, press a button, and repeat until it ends. Sarah Palmer, your Spartan commander and narrator so to speak, is the most grating and one-dimensional character Halo has offered, though perhaps that's intentional.
The list goes on. The monthly challenge, a sort of completable goal that gives lots of XP when finished, has been the same every month since launch. Campaign theater and scoring have been removed. Spartan Ops has no theater either. Killcams don't work in any sort of accurate way. Many of the options in custom games are either missing or don't work. Several objective gametypes that were franchise staples, such as 1 Flag CTF and Assault, no longer exist. Microsoft has some kind of deal with Virgin Gaming, so there is no MLG playlist with competitive settings, nor are there any MLG tournaments in the near future.
Welcome to Halo 4, egghead.