As someone who's coming from an MMO background (played EQ, WoW, Warhammer, GW2, FFXIV, EVE) and not overly impressed by previous Elder Scrolls games (Daggerfall through Skyrim), I feel a bit different than the previous posters in this thread.
Running on a late 2012 BTO iMac (27", 680MX, i7, fusion drive), the game is smoother than any other MMO I've run on the machine. It's actually impressively smooth considering the graphics quality (I ran it at max settings). Their default full-screen mode seemed nice to begin with when it didn't black out my additional screens but the client kept stealing keyboard events (so no typing in browsers on a secondary screen). So I had to switch to a maximised window (which keeps the window borders and looks less than great) which worked better with the rest of the OS. Plenty of bugs in the game itself, with quests not functioning and places where a UI reload was needed to get out of weird loops. Also, proper crashes to desktop every 30-60 minutes, sometimes caught by the Zenimax crash reporter, other times not.
That all being said, I felt the game was very much fun. I had a great time playing over the beta weekend and have since then pre-ordered the game. There's a conceptually interesting skill and ability system and the fact that everything is voiced is quite nice. To me, I feel I will easily put in enough hours into the game to justify the cost (and yeah, it's very highly priced). I'm truly looking forward to playing the game, and exploring various aspects of it. I don't know anything about the end-game content at this point, which will be what decides whether or not I keep subbing after the levelling up process but if they can find a way to keep content fresh and fun (without entirely relying on PvP for end-game) I could see myself spending a long time in the game.
Just the fact that the game runs so well on the mac is almost enough to support the developers for me. I haven't seen any other game able to push the visuals that ESO does on this machine in such a smooth way. It's a clear indication that other games simply aren't utilising the hardware that's available. While ESO isn't exactly state-of-the-art when it comes to graphics, it's certainly outperforming anything else I've seen run on this machine. It feels like I got a completely new machine.