Loniizrath

Elder Scrolls Online.

The whole thing. No part of that game appealed to me at all.

For me it was also this. It just doesn't appeal to me and kind of gives me this "end of Elder Scrolls" feelings, like they just spat out an MMO and said "here's your multiplayer, now run along". I was hoping the next Elder Scrolls was going to take place in, say, Black Marsh, or Elsweyr, since I'd like to know more about the beast races.

Delphene not respecting the Dragonborn.

Elenwen's party.  Delphine made it sound like a really big deal.  I think I would have done a much better job if I was the host.

I don't really have a "biggest" let down, but I was pretty annoyed when I killed the dragon at mount Anthor (near Winterhold) and found my first daedric equipment: daedric boots I then proceeded to jump around and killed myself by jumping off a one-metre high rock. Also when you can't finish a quest.