I loved HALO CE but every HALO game after that has bored the hell out of me. HALO 2 was ok but technically, a total mess. I have never seen worse texture pop-in than in that game and some of the AI (the brutes specifically) were just broken. Halo 3 added literally nothing new except for shiny graphics and ODST I don't know how Bungie managed to fuck that up. It was a fantastic idea, taking the spotlight off of the frankly boring Master Chief. However the story and pacing was atrocious and the decision to introduce firefight but not let it utilise matchmaking just baffled the hell out of me. On the subject of the story, I could have written a better story line than them. Halo Reach had an equally boring story. None of the characters were developed in any kind of depth, except for Cortana and Captain Keyes and only then if you'd played the other games. The multiplayer is fun though and me and a friend have had hours of fun dominating people from a Warthog.
Halo 4 seems to have totally lost it's identity. Irregardless of whether it first invented the 'power armoured space marine' aesthetic, It has totally lost it's identity, it's just caught up in a world of games just like it. As I said to a friend earlier who adores HALO If it wasn't for the title HALO in HALO 4, it would not be getting even half the review scores or praise it is getting now. It has changed little to nothing since Halo 2. In my opinion, and quite frankly it's not difficult to see why Bungie has handed over the reigns to 343 Industries as they have made more money than the entire planet earns in a year. They don't need to innovate, they can just let the game stagnate, as they have been doing for some years now and they'll still make a killing just because they produce a sub-par COD clone and stick the words HALO on the disc case.
I think what really irritates though is how 343 like Bungie haven't changed anything between games, except Chiefs armour (and how the hell does he do that when he's in cryo?) in fact, as far as i can tell, they're just copying COD with the 'Perks' system.
As a final note, some of the game reviews are just a joke. IGN, pfft. don't even bother. They've either been bribed or they just have no sense of a what originality is. The guy who reviewed HALO 4 for then was so excited I thought he was going to upload footage after the review of him shagging the disk. The only roughly sensible review I have watched was on this very website. At lest the guy has the brains to say it's not a spectacular game. unlike IGN and every other reviewer.
Anyway, apologies for the wall of text but this is something that would make me pull my hair out if i had any. To summarise, I haven't always hated HALO. I adored HALO CE but the rest were just terrible and have nothing original or imaginative about them at all past HALO 2. Of course, this is opinion so don't get mad if your opinion differs to mine.
To cap off, I would say none of the games (except HALO:ODST and HALO REACH) are bad per-say, just that they have absolutely nothing unique and interesting about them with Bugie's only saving grace being HALO CE, and that's what got them into this unimaginative and unoriginal mess.