I'm not saying Halo 3 is good or not because i haven't played past the first level. But at the same time it is the only game (apart from Viva Pinata) of the 10 games that i own on the XBox 360 that i just cannot be bothered to play. I don't know what it is about it, but it just doesn't capture my imagination or pull me into playing it. I got 2/3 through Halo 1 on the PC too, but gave up due to it's repetitive level design. It's such a shame - i don't hate it and i want to love it, but i just can't!
P.S. To put my Halo 3 plight into perspective, i even forced myself through to the end of Assassin's Creed after playing the first level of Halo 3, and still didn't return to it!