I was late in the game to Halo. Played the first one, maybe two years ago out of historical interest. I was impressed by it and it made sense that it gave Xbox a foot in the console door.
I'm just playing Halo 3 now and, meh. I might not finish it (I'm on the 3rd chapter of the campaign). It's garbage. I think the reviewers that gave it 9+ were paid off. The campaign is terrible, the AI is an embarrassment, the game play (empty clip, run forward press B) is laughable.
I picked up Halo Wars for twenty bucks on Amazon and played through part of that campaign. It's a solid 5. Kind of a test platform for how an RTS might work on a console. Seriously, MS should just patch the Xbox to support a mouse and keyboard--I'd rather have that than Natal.
I won't buy another Halo title. The franchise is dead to me.