The original Halo was incredible IMO. Lots of people will say that it's just your standard shooter, but I disagree. It really wasn't like anything else I had ever played. I thoroughly enjoyed it on the PC. The campaign was exceptional, and the multiplayer provided me with hours upon hours of fun. I even got into some of the mods that were out for it, and that was even more fun.
Halo 2 I didn't really like quite as much. I thought dual wielding was a terrible idea, but most people seemed to like it. The BR was a great addition though, and it remains one of my favorite weapons ever put into a video game. I had it for Xbox, and I never got the online service (whatever they called it back then). I just played it with my friends at parties and stuff. Still lots of fun. We would always play rockets on that one map... I can't recall the name but it was the one you unlocked by beating the game. It was a giant circle with a giant pit in the middle, and there were four rooms equal distances from each other on the outside of the circle. Simple map, yet I couldn't get enough of it.
Halo 3. This is where I got ridiculous with it. I really didn't like it at first, but then I befriended this one guy who was just exceptional at it. He could embarrass kids all day in any playlist. I swear he could have gone pro and made tons of money playing that game. He taught me all the little tricks, like how to get around the maps, all the little routes that you could use to juke people, how to properly use the BR... oh man. I remember my first ninja. The poor kid thought I was a hacker because I proceeded to do it to him three or four more times that game. I got pretty damn good myself, and we even had a four man MLG team going for a while. We were all pretty good, and we had very good teamwork. Not quite cut out for tournaments, but we still had TONS of fun. We even went to a MLG tournament over at Gaylord Palms. I still can't believe I did that, but I don't regret it one bit. Watching those teams go against each other, hearing all the constant call outs... those games get really intense. I think BTH won it against TD, which I wasn't too happy about. I continued to play all the way until Reach came out. I was sooo excited for it. Then...
I played it. What the hell is this crap?! This isn't Halo! I mean, it is, but it's not... I don't know how to explain it. They tried to mess with an already great formula, and they just screwed it all up. The campaign was fun, but that's it. It didn't fit into the storyline of Halo at all. They tried to say that they were Spartan III's, but those didn't come until AFTER Reach was taken over by the Covenant. The graphics were improved over Halo 3, but I feel like they could have done a much better job with it. Nothing really looked Haloish. Still really bright and colorful, but that's it. The DMR just wasn't the same. The new hit-scan system took away from the skill that Halo 3 required. I just feel like they dumbed everything down so that little kids could play their M rated game. Also, how can you have a Halo game without that ridiculous jumping?? That was one of my favorite things about Halo! Sniping in Halo 3 took quite a bit of skill to get a good streak going, but in Reach it was a piece of cake. The map design in Reach is atrocious, but not as bad as the spawning. Whoever came up with Reach's spawn system is smoking some serious crack.
Now Bungie is out and Activision and 343 are in. I'm not really sure how that bodes for Halo 4. While I'm glad somebody other than Bungie is behind the wheel (since they messed up so bad with Reach), but putting it in the hands of the publisher who makes Halo's #1 competitor? That doesn't make a lick of sense. I really wish that they would have just announced Halo 4 and ENDED IT. Bring closure to the story, put your own probably COD-esque spin on the multiplayer, watch all the die hard Halo fans break their disks in half, and then go back to making the most mainstream, standardized, easy to play shooter to ever hit retail shelves. I honestly don't even want to see Halo 4 come out. I would much rather see what the film industry can do with the franchise.
If you want some REAL Halo enjoyment, read Eric Nylund's books. They really put the story of Halo in perspective. I know the story isn't exactly original, but it's compelling and interesting (in the books). Fall of Reach is my #1 favorite book of all time. I am halfway through Ghosts of Onyx, and it's almost as good. Lots of action. Some of the shorts in Halo Legends are pretty entertaining too, especially the comedic one featuring "Spartan 1337."
Oh, I forgot about ODST. Whatever, I didn't really enjoy it. I mainly bought it for the multiplayer disk with the extra maps. I even went through the trouble of getting those Vidmaster achievements so I could wear my silly recon armor. Yeah, I was THAT into it.
Sorry for the extra long post, but Halo has been a very big part of my life (sadly), and I just wanted to share my thoughts on the subject.