It is difficult to explain and quantify. I can equate it to the new bike feeling, that's the fast feeling that you get when you ride a new bike for the first few times. Somehow it just seems to go better than your old bike. It feels like the big wheels roll faster and easier over the rocks and the bike feels very stable.
Don't be fooled though a 29er hardtail is no replacement for a 26" full sus, 0" travel just isn't the same as 4" travel no matter how big the wheels.
But the big wheels sure are fun to ride, even if they are a bit heavier.