By far the biggest change is the HST transmission. In the 4300, the hst pedals directly controlled the hst an were very stiff. It was difficult or many women, and really got tiresome for most folks (I am speaking from limited experience, owners might chime in to say it's no big deal...)
The 10 series went electronic on the HST and the reverser.. The HST requires far less effort on the pedals. The new reverser allows the user to adjust the speed that direction changes take.
There are some less apparent changes like in the front axle.
The eHydro also added a few handy features, like increased ergonomics, placing the controls in a very handy layout. There are some other gems like MotionMatch (like the eReverser) and LoadMatch which controls the transmission to reduce stalling under load.
The big deal:
If the 4300 is a syncshift, there is little to differentiate it from the 4310
If it is a reverser, it won't have the MotionMarch
If it is a Hydrostatic, you might not like the pressure required by the pedals.
4300s can be 2wd or 4WD (MFWD in Deere Lingo) There is NO DEBATE here, you must have MFWD (anyone arguing this point will be shot /forums/images/graemlins/tongue.gif )