The main changes are
Voice control, however you do need to wire in a seperate mic for this. I have it and hardly use it as it is quite slow. Earlier versions had it but it was improved from 38XX onwards.
When you hold setup for 30 secs you get the FM, AM and Version Info menu's. Version info gives you map version, hw and sw versions
New style compass
New POI which you can load from SD Card
Third partition for the POI's, Music partition becomes 15gb unless you have one of the newer versions which has a 40gb HDD like i do.
Stability improvements
Faster startup over 2XXX firmwares
Display optical parking and rear view camera at same time
Display climatronic control if approriate climatronic fitted
Excluded roads in route options menu
Larger RVC screen with transparent menus at the side
That's about it off the top of my head.