I like the idea of a wholly seperate multiplayer game. TES Online or some such. But I don't want TES V to be multiplayer.
If multiplayer is done right, it could be a lot of fun. to be done right, it would have to have seperate servers for PvE and PvP, so people who don't want to be ganked can do PvE and people who relish sudden attacks from players can have their fun, too.
Dungeons should be instanced, and it should be easy for people to find groups. WoW's dungeon finder works quite well for this.
I think a Mortals vs. Daedra model allowing playable Daedra would be outstanding.
Roleplaying servers should be available, and roleplaying should be enfored. You can do whatever you want otherwise, but on an RP server I don't want to see 'Martinseptim' 'Daaedraaslayer' or 'Dagonnn' running around on an RP server.
Also, while free to play is awesome in theory, you run into the issue of someone having better gear than you do because he can afford to shell out 25.00 for extra goodies and/or content. I would prefer a subscription fee with all content being available.
A lot of people's bad opinions of online play is the result of:
A few idiots runing it for the rest. Bad apples and all.
Poor game model (Ultima Online and Meridian, I'm looking at you. Whoever came up with PvPers can steal your gear and you lose your stuff upon dying should be shot)
Obstruse or overly difficult magic systems or crafting systems (*cough* Runescape)
Quests like 'Bring me 20 bear bums!' o you kill twenty bears, and maybe 2 bums drop, which is annoying because they obviously have them
Mind, those quests can't be avoided altogether, but they should try to make sense.
No one MMORPG is perfect, some do it better than others or are just more fun despite the flaws. I think Bethesda could do it well if they avoid most of the crap that makes for poor MMOs that isn't player-caused.