I have been a online d2 playa since early 1.10, and made it to the top levels of Pvp; the best thing about D2, for me, was the intense funpk and clan officals.
-Lets face it it, after you beat the story a couple of times, the thing that kept people playing was the desire to be dominant in PvP, this desire it what fueled all those countless baal runs/ mf runs/ trade games and g rushes. PvP is wat kept D2 alive for all these years and i hope blizzard can recapture
-I think the large skill/gear gap made PvP so great in D2, there was someone always better than you and you really had to work hard and practice to win pvp. I DONT think BLizzard should decrease this skill gap; i think if blizzard caters for the 'casual' gamer to much the pvp will be ultimatley empty and unsatisfying. The fact that it was hard to dominate a 'pub pk' is what made it so rewarding.
-Perhaps a Pk areana which betting/spectacting/clan options are available could be used to cater for competive Pvpers, whilst a 'Pot luck' areana could be set up for casual player parties which could randomly select a gametype like 'face waves of monsters', or 'first person to kill 30 monsters', etc.
-There should be still some skill required to PvP, (like name and chainlocking in D2).
-Clan features for players who have finished the story mode or something.