After playing the demo through 3 times (Easy, Easy while exploring/appreciating the graphics, and Hard)... I'm so fucking sold. It was honestly going to be rental for me, as I'm short on cash and not too fond single-player only purchases, but wow...
Combat: You can check my previous posts as to how worried I was about the gun combat being boring, but all of that changes once you are actually in control. I wouldn't call the AI smart, but they are extremely aggressive and constantly change positions. On hard, I had to observe the entire field of players - if you focused on the position of one guy too much, additional enemies would flank, and your initial target would throw a 'nade to flush you out towards them, forcing you to retreat to previous areas of cover. All three times I played through the demo, I found myself in different areas of cover... so the combat itself is pretty dynamic, forcing you to think in the moment rather than planning things out ahead of time.
Platforming: As for the 'platforming'... what little there was, I enjoyed it quite a bit. The segments available in the demo weren't platforming in the sense of tricky timing, it was more of a 'I have to get there - how do I do it?' You could get clues as to where to had to go by pressing L2, but there aren't over-exaggerated elements of the background that hold your hand through the environments. The game itself is linear, but there was at least one point where alternate routes were available to get to the same destination - and like I said, it doesn't feel as linear as it is because they don't hold your hand from place to place like some games do (God of War is an example of hand-holding for me).
We've all seen the graphics an animation, so I don't need to comment on that in 'detail' - however, I will say the textures were much better than I recall them being from previous shots and videos. Some of the ground textures are simply amazing...
EDIT: And I have to note, you can jump from cover to cover... I saw a few people mention that you couldn't switch cover quickly and was disappointed to hear that, until I did it myself. Once you are locked onto a form of cover, just point in the direction you wish to go and press circle - it's even context-sensitive to the point where it allows you to change from high cover (a wall) to low cover (small block/box, etc) and vice-versa.