Wasn't WoW out then? What about CS-Source? Everquest? Starcraft? L.O.R.D? Battlefield 1942? UT 2004?
I only list so many games because you painted such a broad stroke:
Overall Halo 2 was the best online multi player game at it's time due to its customization
I personally prefer gameplay to customization, so I don't concur with your statement that Halo 2 was the best online multi-player game. I have played it, and while the vehicles and weapons are kinda cool, the gameplay itself is just so stale. Garoth is right, Tremulous is much more exciting. Hell, Team Fortress Classic is more exciting than Halo 2.
Sorry if it seems like I'm hating a bit...I try not to do that anymore. It's just when people really push Halo 1/2, I usually find out they haven't played a lot of other games. I'm not saying this is the case, but this isn't the first time I've had to defend why they're not their not (or were not) the greatest games ever.