I've played a lot of MMOs over the years, and often circle back on some of them when they have expansions. I play all of the WoW expansions, for example, but once I use up the new quests and hit the new level cap, I unsubscribe again.
I looked at the ESO classes a little, and it's interesting that they're saying it sets a few of the skill trees for you, but there are many others that are open to everyone, and the gear is not class specific either. So it looks like they're still aiming for more customization than many other MMOs.
This video is old, so it's probably a bit out of date:
Anyway, part of me is still tempted. I haven't played through any of the other Elder Scrolls games, so I'd be coming in fresh.