Well the "last one" was Tony Hawk Underground 2 which didn't offer any online modes, just multi on the same console.
I haven't played much so some of this could be incorrect ...
basically 2-8 players in a particular level (the story mode "LA" gets broken up into 8 or so separate levels outside of story mode)
And there are various games you can play I think there are about 6 different games, you have your typical Score attack where the player with the highest score at the end of the run wins, then there's a "Grafiti" mode where you do a combo off of an obstacle(s) and the obstacle(s) are painted your character's color, if someone else wants to steal an obstacle they have to perform a higher scoring combo on it then you did and if they do it will change to their color. The person with the most things painted in their color at the end of the round wins.
There are several other modes to, it's pretty fun really. Basically this is how the older games did multiplayer, but THAW is the first time it's been multi over LIVE.
I haven't really explored the multiplayer much though.