OK, I played the demo for the first time last night..... and loved it.
I don't play a lot of shooters, so it took me a little bit to get adjusted, but it's a lot of fun. Visuals are great - you really do feel like you're just wandering around in the jungle, and the characters look like CGI. Half the time you can't even figure out where you're going, because it's not mapped out really clearly like most games are. That might sound like a negative, but I thought it was pretty cool, because it makes it feel less "contrived" than most games. If you crash land in the middle of a jungle in real life, you're not going to have clear directions on where to go. You have to climb up on vines, ruins, etc, and kick down a few gates to get through to where you're going.
The best part of the visuals, apart from the character models, is the water. It's everywhere, and it looks like actual water. When you get in the water or walk under a waterfall, Drake's clothes get wet, and then they dry off as you're walking around. If you walk through shallow water, only the part of him that is in the water gets wet.
Only two things that I didn't like about the demo:
1. When you're getting close to dying, everything goes to black and white, which is good because you know you better look for cover, but it makes it harder to see the guys you're fighting, so unless you can hide somewhere they can't get to you, it's tough. During normal play, the colors are so vibrant that it's easy to pick out where the enemies are.
2. The demo was just a few areas of one level, so while it really gave a good taste of the fighting part of the game, it was hard to tell what the game as a whole will be like - i.e. what is the point, what things do you have to try to find, figure out, etc. But that's just a complaint about the demo, not the game itself.
Overall, playing the demo has not moved this game from the top of my wish list - it looks to be a ton of fun...