What can it do is a broad question all right...it has more to due with the driver than the rig most of the time.
Without skids or armor...you can do fire trails and other terrain that is short on sharp rocks or protuding stumps...unless you are good at picking lines through the stuff, etc.
Mud is best done with mud tires...but AT's are a decent compromise for a daily driver...w/o armor, rocks are a bad idea.
You can cross headlight deep water...and hill climbs should be no problem...watch the off camber stuff if its bouncy...but, you can heel over really far w/o tipping....find a slope, and get one side up on it...and keep going further up on the one side untill you think you might fall over...get out, and try to push it over...it probably won't budge (If it falls over, you were braver than most newbies...so as a rule of thumb...if you open the down hill door, and it doesn't swing into the ground...you can go further over...the door thing isn't the limit either...but at least you won't bother to get out and push if the door isn't even hitting the ground yet...)
(Tie a tow strap as a safety line to keep it from going over if it makes you feel better/keeps you from suing people...etc...)
As to pre-'05's...
The 2000-2001's have square headlights and smaller wheel wells that barely fit 31's w/o trimming...
the 2002-2004's are mechanically pretty much the similar, but have round headlights, a higher hood line, a slight power boost, and can be supercharged, and have slightly larger wells due to a bit less plastic in the way...
The 2005+'s are a completely new design, and have WAY more power, can have a factory locker instead of the previous LSD, and more computer gizmo traction stuff, more passenger room and cargo accomodations, have different axles and differentials, have front coil spring suspensions instead of torsion bar suspensions, and can fit 33's stock.
There are of course other differences, but the above is a good start.