1 & 2 vs 3 & 4 are like night and day. It all boils down to the pacing. More mixups are apparent in 3+4 and running into random high/mid/low/throw is much, much more common and a viable way of attack. Also there's much less "stunning" moves in the previous 2 installments.
As it's been said before
1 & 2 focuses more on standard moves, poking, and throwing.
3 & 4 focuses more on well placed specials, and running high/low/medium/throw mixups.
Simply put you do a lot more running around in 3 & 4, and do more pace setting in 1 & 2. Running like a maniac in 1 & 2 on a rising opponent will just get you killed :P
I do believe that more standard move will link to each other in SSII (althought it's not easy I'll post up the vid on my website if you want it)
UnCauzi
www.fierceslash.com