This is an amazing ride that every PS3 owner should play.
Things that are new in Uncharted 2 compared to Uncharted 1:
1 - Better graphics.
Uncharted 1 had some mind-blowing visuals back in 2007, but in 2009, Uncharted 2 stepped up the notch immensely and practically used up every ounce of power that Sony's Blu-Rays have to offer. The graphics and animations are top notch compared to any video game I've ever seen. In fact, when you play U2, you'll be looking forward to the next cut-scene just because the graphics and animations are so good. Heck, you'll just want to stop and look around Drake's environment and take in the highly-detailed world about him every so often. It's that good.
2 - Longer Story
Yes, Uncharted 2 has about 5-6 more chapters than it's big brother, which means you'll be spending more time in front of your screen which means more fun. But it's not just about more chapters in the game; U2 has more variety in its levels from snowy mountain tops to a foreign city to larger-than-life temple ruins. Drake is all over the place in U2 as opposed to U1 where everything took place on a single jungle island, which isn't a bad thing, but a treasure hunting adventure game that takes you to a lot of different places is a nice change of pace.
3 - More Characters
There are more characters in U2 than in U1. In U1, we were introduced to the main three; Nate, Sully, and Elena. In U2, you run into more characters that all play important roles in the story as it unfolds. Not to mention you have more skin choices in the 'rewards' section.
4 - Different Reward System
In Uncharted 1, you had to rack up a certain amount of points in order to unlock rewards in the game. In Uncharted 2, every time you complete specific tasks like collecting a hidden treasure, you'll earn 'money' which you can then spend in the 'store' once you beat the game. So instead of earning points, you earn money which you can spend on rewards like character skins, weapons, etc. I think this is a much better approach than in the first game, which depended on you getting a certain amount of points in order to unlock rewards which could take a while.
5 - Stronger Enemies
In U1, the only enemies Nate had to fight were mercenary pirates (and those scary ghoul creatures). They lacked sufficient armor and only had a few weapon types at their disposal. In U2, the enemies are actual soldiers in body armor with bigger, badder weapons, and it's gonna take more strategy and skill to take these guys down, not to mention a lot more ammo. New weapons in U2 include RPGs (kinda like a bazooka), heavy machine guns, crossbows, and a better way of throwing grenades from behind cover. But no need to worry, you'll have a lot of fun with these new additions to the Uncharted series. The levels are more intense this time around too, so there's no messing around during the gunfight parts.
6 - Online Multiplayer
In U1, there was no online multiplayer, not even a co-op mode for 2 players. In U2, Naughty Dog gave gamers both options, and they are a blast. You can easily spend hours alone in the multiplayer, it's that good.
In Ucharted 2, Nathan Drake becomes entangled in a quest to locate the legendary city of Shambala, a place where one could live forever thanks to a mysterious 'stone' that is believed to be the source of such power. A ruthless Russian and his army are after this 'stone', and it's up to Drake to stop him and mow down his forces before things get out of hand, in which case they do, but I'll let you find out the rest of the story for yourself. Overall, this game has everything you'd expect in the sequel to an already amazing game. The only thing I was kind of disappointed in was that Sully only shows up in 1 chapter in the entire game and then you don't see him again until the very last cutscene, but other than that, I enjoyed the game a LOT.
So there you have it. If you haven't played Uncharted 1, I suggest that you play it before delving into Uncharted 2. Believe me, it's a fun game despite what people say. And when it comes down to it, I don't think that Uncharted 2 is 'better' than Uncharted 1; it's just another great game by Naughty Dog that continues in telling another great story. The way I look at U1 in comparison to U2 is that it's kinda like Super Mario Bros on the NES - everyone knows it and likes it; it's legendary, but Mario Bros 3 is considered a better game because it has better graphics and a better story, if it has one. Anyway, enough ranting... I would HIGHLY recommend you purchase the 'Greatest Hits/Game of the Year' edition of Uncharted 2: Among Thieves, which comes with over $35 in DLC for the online multiplayer mode. I got my copy brand new for $26 online, so it is well worth your money. TWO THUMBS WAAAY UP! :))