Through play.com's pre-order system I got access to this online beta, and believe me when I say it may be the best thing I've ever played. The graphics are completely mindblowing! Take MGS4 or Killzone 2 or any of these and forget them graphically, Uncharted 2 is clearly the new benchmark.
The matchmaking system for this multiplayer beta is a bit rough. It can take minutes to find a game sometimes, so much so that I've been forced to quit and go play something else, but once you're into a game it's definitely worth it. With a climbing system very similar to the original game and maps that have clearly been laboured over you get a completely different online experience to anything else.
One level sees you in some kind of Chinese village in the pelting rain where you have a choice of sticking to the ground, running between cover (the cover system being very similar to the last game, and 360's Gears of War) or you can go high, using your climbing abilities to get to great sniping oppurtunities.
Even watching the trailer for the singleplayer got me all excited. This is going to be the Playstation's definitive title of 2009, and if you don't own it then you're missing out. A must buy for me.