I'm assuming you mean play as big boss?
That would be a yes/no. You play as "Snake" the man who becomes Big Boss later on. 'Course Kojima San is a tricky guy, who knows until next month.
/my experience...
So the demo boots up, and I'm very impressed with the graphics. Japanese voice overs for the demo, so I can't really comment on the voice acting, but if it's the same or better quality of previous we're going to be in for a great experience.
I notice during the first cutscene of Snake skydiving, that there is more interactive portions to them. Instead of just being able to zoom, some portions you are also able to switch to first person view mode, to see what he's seeing. It's really cool during later portions of demo when he's using binoculars to spy enemy positions.
Enemy AI is scary real. 'Nuff said.
I'm thinking the difficulty level is severely dropped for the demo. It's far too easy to hide, maybe the option to remove the camo index from view will make it a little more risky/fun in the full game.
Eating as far as the game goes, it doesn't immediately restore health like it used to. It's used to restore stamina, which while you're resting, restores health. Much improved over the old way of doing it. Of course there's a health restoring medicine that works similar to the old rations, but less effective.
That is all, unless there's going to be questions.