I like Uncharted 1. Let's get that straight before I say anything else. Because it does make me slightly biased. But that aside, Uncharted 2 among thieves really ups the ante. The graphics are slightly better, everything is more smooth and the free running/climbing is really more integrated into the world.
The multiplayer beta is just what it sounds like, a demo that only showcases multiplayer. And its a lot of fun. Gameplay is engaging even though it's quite slow compared to other shooters. The levels are pretty large and since you can climb you have to think vertically unless you want to get shot repeatedly by the other players climbing the ruins.
There is a modern standard leveling system and a matchmaking system that we really don't know much about since there aren't that many players playing it.
So far though, the beta has me convinced that the game itself is holding up to the hype. Still, Uncharted is just as much about the narrative progression as the game mechanics. And we haven't seen them yet.