It took me a while to get drawn into Halo for some reason. I think it might have been the slow pace but I never really got into it until everyone else had already let it start collecting dust on their shelves (if that's even possible). I bought an XBOX the day they came out, along with Halo and a couple other games, and I took it to a friend's house and we marveled at the nice pretty graphics and stuff but I never did play past the first level the whole time I owned my XBOX!! I then sold the XBOX and a few months later bought a used one on eBay because I missed playing a few games...everybody was STILL talking about Halo and how great it was so I was like WTF I'll buy it again and give it another chance--apparently nobody that owns an XBOX should be without Halo...
After I bought it the second time, I started the co-op campaign and was sucked in hard and fast. A friend of mine came over against his girlfriends wishes (LOL) to play Halo until we finished the game, and we did. I loved every minute of it.
Greatest game EVER? No, not for me...but it's damn good, especially by console standards. I think the game was just a bit overrated though because I've rarely seen a game that will make people "OMGjiZONIT" like Halo does (well maybe CounterStrike and Everquest, haha) and I never got so attached to it that I couldn't live without it or stayed up night after night after night after night after night playing it. But then again, I never played too much of the multiplayer portion aside from co-op so maybe that's what I missed out on. I liked Halo a lot but it won't be too hard for me to move on and enjoy other games like Far Cry and DOOM 3.