You're about 5 years too late...I'm just sayin is all.
Certain games just click with people. With Halo, the multiplayer is what really grabbed people and had them playing for hours upon hours, and having people over for Halo LANs. Not since Goldeneye had people experience a truly great console FPS multiplayer experience. The SP is a bit weak, but not nearly as weak as Halo haters try to make it out to be. I've played through both the Halo 1 and Halo 2 campaigns several times and I've enjoyed my play through each time.
I can see why PC gamers don't see what the fuss is all about, I play on both PC and console, but have recently preferred console because PC gaming has gotten stupid expensive. PC gamers play these games with better graphics, better controls (arguable), better network capabilities, and better communities (in terms of mods, etc) so of course they play Halo and go "What's the big deal" And they're right.
But for console gamers, it's different. Rarely do they get to see a FPS as popular, and as playable as Halo. Think about it. The 3 big console FPS multiplayer games that have been released are Goldeneye, and Halo 1 and Halo 2...3 games over a 10 year span, that's pretty pathetic. I'm not saying that these were the ONLY games people played, but I think everyone can agree when I say that these are the main 3 people play(ed).
I also happen to disagree with alot of people when it comes to the details of Halo. The graphics were great for their time, the gameplay had enough different gameplay scenarios to keep it interesting (save for the last few levels), and though the guns were weak, the big 3 (the AR, pistol and shotgun) were great fun to use, not to mention the frag nades and oh so fun sticky grenades.
And anyone who tells you that Halo is their "first" real FPS should be taken out and shot because they're probably 14 years old and didn't start gaming til the late late 90s. I am a HUGE Halo fan, and while I can see people's problems with it, I simply disagree with them.