: Campaign: Bad enemy design
The Promethians are hardly the worse enemies we've fought, H2's enemies were far worse, and H3's flood to an extent as well.

: Bad level design
Like what? It was certainly better than Reach's mash of firefight and multiplayer maps.

: Bad writing
Compared to what? H3, ODST, Reach? H4's story has some issues, but it is presented very well, probably the best in a Halo game since H2. If you like the story or not is another issue, but I enjoyed seeing more of the character of Chief and Cortana throughout the game, and learning more about the Forerunner and exploring a new forerunner world. Not to say it was perfect, but I did (and many others) enjoyed it.

: Invisible walls
All games since H1 have had these and it's a necessary evil given how massive environments are these days. Destiny suffers from this too.

: Multi: Custom loadouts
: Ordnance
: Armor abilities
: No red Xs
: Bad maps
: Dumb new medals (single kill? Really?)
: Horrible gametype changes
: Imbalanced
: Several custom gametype options were either missing or didn't work
There are certainly legitimate complaints to all these points, but it doesn't mean the game is bad, it may not be your favorite of the Halos, but it's still one of the better MP games out there. I'd take it any day over half the stuff I have on my shelf, many which are other AAA games.

: Both: Worst UI ever. Of all time.
Yeah it's pretty bad.

: Sprint
I think most people loved it's inclusion, there are certainly some pros and cons as to having it though.

: Slight bloom (on DMR)
There was also slight bloom on the Halo 1 weapons... just not visual. The DMR is still a great weapon with it, and in fact needed an update on it because it was initially to OP?

: Flinch (as opposed to descope)
Personal preference, but I can see why many people don't like it. I prefer descoping too.

: Shitty online stats
: Cut features: Playing as an Elite
: Campaign theater
: Zoom/percision control in forge
: Firefight
: Rendered films
: No screenshots on their website (at launch)
: No in-game file search (at launch)
: Several popular gametypes were cut
: Several emblems were cut
All legitimate complaints.

: There's probably a lot more I'm blocking from memory.

Like any Halo game H4 has it's issues and it's problems, many which come down to personal preferences. But it's not a trainwreck of a game, I'd argue H2, Reach and Destiny have many more issues throughout the SP and MP portions than H4.