Based on the demo. I approached this game with some trepidation, having not enjoyed much success (or enjoyment) with first person games in the past.
The physics are well done. Although you spend most of the time having no view of any part of your body, knowing when to jump and grab is highly intuitive and although not easy, it's not too hard so that you become frustrated. Controls are simple and quick to learn and it utilises the SIXAXIS well for things like balance, rolling, basic combat (though there are button-press alternatives). The combat is either very easy or extremely hard - one gets the impression that the developer would rather your run and evade most threats rather than turn and fight.
The environments are stunning: think le Corbusier in cold colours punctuated with vivid tones. You have a lot of freedom to roam and choose routes, but if you do get lost and need a pointer, you can press "O". Add a great soundtrack and it all adds up to a highly engaging and immersive experience.
In ten minutes I went from "I'll see what the demo is like but I usually don't like this sort of thing" to "I've preordered it and cannot wait for it to arrive".