First, let me say that I first played Halo 2 on XBC. It was great but the lag was quite annoying. I then found Kai, which was IMO much cleaner and straightforward. Then I decided to activate my 2-month free trial. My clsoe friend simultaneously did the same. We were addicted to it. Virtually no lag and you could find games quick. I decided to get a year. I didn't renew at the end for several reasons:
1. Most of the time I played, there were standbyers and modders.
2. Near the end of my subscription, Bungie cracks down on cheaters. All's good, until I am at ~level 30 and I get bridged every single game. In Xlink there are a couple of modders, but they usually don't go into other people's games. There will be an occassional asshole(i.e. Blue Tooth), but there aren't many.
3. With my crappy comcast connection (4 mbps down/384 kbps up), I would never get host and as a result, I would get cheated every game.
4. $50 a year for one game. Yes, I'm cheap, but I can't help wodner some people play 3 or more games on XBL, but still pay $50 a year.
6. Utterly dumb games implemented in MM. I mean I never get SWAT which I'm great at, but now I have to play landgrab? Yes I know about the Team SWAT playlist, but that came afterwards. WAY after most of the fun was had. In Xlink you can choose what to play with no fuss.
7. Ranks. Somebody quits on your team and you feel frustrated. In Xlink, people can join and leave as they please.
8. Friends list. With XBL you may think you're closer to people with the friends list, but not really. In XLink, you get to play with the same people for many games. On live, this was not the case. Getting a custom game with frineds up and running is such a hassle.
9. Little kids. The perecentage of whiny little kids on Xlink is much less than XBL, and even then many of these kiddies can't afford mics.
10. No modding custom games in XBL. Occasionally some "good" modders come to XLink and have mods which give special abilities to everyone in the game. It's quite fun. The host set it to magnums , no shields, on midship. The weird thing was the magnums would hit someone and they would fly across the room with more force than a rocket impact. If you shoot the floating platform a couple of times it moves like crazy and slants to one side, so you can jump to the platform from one of the big rooms.
Shortly after giving up XBL, I disconnected my Comcast internet and got Verizon's FiOS(5 mbps down/2 mbps up) and can now host 16 players on Xlink with no complaints from either me or the other players about lag. If you find a good server, then there is no lag. I can even host people from Mexico with no lag(I live in Maryland).