This were basically the (optically) visible differences.
Ex2 has had the problems of tons of exploits that were possible - but were fixed in SEP.
On the other side, Ex2 still is said to have the better melee experience.
Item drop was cool, but still... unbalanced. Think of a Pred with storm shield and a rocket launcher or pulse... :/
Much of the eye candy in Ex2 may be seen in XR - it would at least be the right place to be seen.
CPU-Usage for servers were lower which allowed higher player counts for the same cpu usage - but bandwith usage was much higher than SFE
Ex2 limits to 64 players (the default S2 Savage1 game limit) and got somewhat unplayable in a virtualized environment with more than 56 players (lagz0r)
On the other side:
Server panel ingame was cool - hope to see that in XR too - same with clan server.
Simply join it with your team mates and have a graphical interface to let them join. Once they were in, you could manage them yourself. Quite easy and straight forward stuff...
So yea - as Jebus called it: Ex2 was Savage(1) with balls on. Too bad he didn't put the same energy into bug-/exploit-fixing. - And too bad that WoW carried him away...