I got an invite to try it out this weekend so I gave it a go. Played for about six hours because that's all I could take. So far it is extremely disappointing and there's no way I'm paying $15/mo for that game, never mind $60 up front. For an MMO it feels like you are playing in parallel with your party members rather than cooperatively. For instance, one quest we were on, despite working together, had to wait for our own set of refugees to make it through an area. Mine ran through about a minute after my friend's did. Talk about killing immersion. Then there's the whole "stand around and wait for the quest boss to re-spawn because someone else already killed it. I'd much prefer a guild wars type model where you have a common town and the other areas are instanced. I know that takes away from the MMO feel, but it allows for greater immersion. Another issue I have is with the combat. It's just plain boring. Nothing else to say really. At no point did I ever feel engaged in combat or feared for my life.
I think the ideal multi-player experience in an Elder Scrolls game would be similar to how DQIX works. You can join a friend's game with your character to advance your character, but only the host's story line advances. The guest player would more or less be a companion. This way you can keep the persistent world and that feeling that the world revolves around you, the main character.