I have been playing ESO since one of the first betas, and there's so much to love about the game. However, one of the biggest drawbacks was the Muppet facial animations. That said, the way the conversation UI is setup, your eyes pretty much always divert to the dialogue subtitles and responses half of the screen, rather than focusing on the NPC.
This was good because I would generally just read the text and select a response. The NPC was there, but really just a background fixture, rather than a vehicle to drive the plot.
HOWEVER! Now that the facial animations are much, much better and the NPCs can emote more, I find that the UI is in need of a change, whether it be optional or not. The NPCs now are able to portray far more and they're interesting to talk to.
My suggestion is this: rather than have the screen essentially split in two, why not have the option to center the NPC and dialogue (much like we've seen in Bioware games and Skyrim). As it stands, NPCs are being ignored (as is the hard work of the animators!) and the game is less immersive, as a result.
I think this would go a long way in bettering the game. One thing that would also be a great addition is the ability to turn off subtitles. I often fall victim to reading an NPCs conversation far before they actually communicate it, which makes what they're trying to say far less impactful.