I only got to chapter 9 this weekend, and I concur, best gaming experience ever. From the opening platforming sequence and cut scenes, you know that this is going to be something special. My girlfriend, unfortunately, has a limited attention span for watching me play video games, though I might be able to pull her into playing herself sometime on the Very Easy difficulty setting.
Maybe it's partly because I played through U1 five times, but I'm finding the combat easier (playing on Normal) but locating treasures harder. I got 9 in the first two chapters and thought I was doing really well, and then in chapters 3-6 didn't find anything, though I scoured every nook and cranny and climbed every climbable. I thought my game was glitching until I picked up a few more in chs. 7-8.
I do have the ultimate cheat, however: the digital treasure map I got as a pre-order bonus from Amazon. It's an interactive map of each chapter and when you click on a treasure location, you get the video clip of Drake finding it, just like you see posted on YouTube for U1's treasures. Pretty handy and nicely done, much more than I expected as a pre-order freebee (file size is 772 MB). I will only use it as an absolute last resort (after I've gone through the game a couple times), and so far I've only experimented with it by checking out the first treasure I had already found. They could really make some $$ off this if they offer it as a buyable DLC, even though I'm sure the content will find its way to YouTube if it hasn't already. U2 will bring a lot of new people into the franchise, who might be drawn to something like this.
Edit: OK, turns out digital treasure map only gives you the location of the first six treasures. What a joke! Thanks for nothing Amazon!
Edit 2: So I complained to Amazon about their lame-o pre-order bonus and they threw me a 25% refund bone. Nice!