They revamped many of the monsters, along with a couple additions of some monsters, I belive. I can't give you anything more detailed, as I only have the 3.5 ed., but I'm sure someone here can.
As a DM I like the damage reduction rules, but as a player I think they suck.
There are a lott of differend DRs, it obligates a character to hold on to a lott of weapons; good, lawfull, adamintine, silver, bluntoning, magic, non-magic... you name 'em.
From a DM-point-of-view I think they suck aswell. You can't bring out to many different high CR-monsters at a time anymore, because it could end in a TPK. You are stuck with many of the standard monsters, for game-balance-sake...
Broken promises
"They made us many promises,
more than I can remember.
But they kept but one -
They promised to take our land...
and they took it"
what about grapple? i am far from sure, but i have noticed a lot more monster with grapple than in the 3.0. but again, when i played 3.0, i was a noob, so i may not have noticed...
if you have the 3.0 MM, i see no point in buying the 3.5 version.
I once had a little teaparty, this afternoon at three, twas was very small, three guests in all; I, myself, and me. myself ate up the sandwhiches, while i drank up the tea. twas also i that ate the pie,and passed the cake to me
You can find an update booklet on the Wizard's site. Just go to Downloads and you should see it there. It's not exactly exhaustive, but it's a good start!