All thinking creatures get 1 feat at first HD and at every HD divisible by 3, no more wierd individual formulae for different creature types.
No more beasts, they are now animals.
Shapechanger is a subtype, not a type.
Lycanthropes changed significantly, no longer have overlapping form stats but now stackable animal and humanoid HD.
Constructs get bonus hp based on size, oozes don't.
LA included in monster listings. Some changed (duergar are +1 instead of +2, etc.).
Humanoid base statblocks are for NPC stat arrays, not base 10/11s.
grapple/BAB included in monster stat blocks
XP awards modified slightly so lower level characters advance quicker than higher level ones from the same party.
Stat boosting items and a few others changed in price.
Staves allow user's stats for caster level and DC.