Halo? Are you serious? Halo is not the greatest anything. It's a series of decent shooters that is inferior to a long list of titles in its own genre. The only thing it does well is multiplayer, and even then games like counter-strike do it better.
Man, call it what you want. But I've sampled nearly all of them and nothing,
nothing gave me the level of immersion that I got from the Halo games. Even the stunted sequel that was Halo 2 had this ability to flow seamlessly between gameplay and cutscenes in a way that revolutionized the whole gaming experience for me.
No other game that I've sampled has come close to achieving that level of streamlined storytelling. All of the others feature abrupt interruptions between gameplay and cutscene that are just downright distracting, and, quite simply, ruin the illusion.
Graphics? Sure, they were lacking. Even in Halo 3, which was dumbed down in order to make up for all that was going on onscreen, as well as to maintain the overall look between all three games.
Overpowering supercharged uberweapons with no basis in reality? Also lacking. But the weapons we got felt genuine. No eye-rolling here while firing off the resident BFG and exploding everything on the map. Halo never had a BFG. Halo never wanted a BFG. And Halo never needed one.
The only other game whose sequel I look forward to nearly as much has to be the sequel to Donkey Kong 64. For that, even I would buy a Wii.