Well. They are an integral part of the TES Universe. Similar to Dragon Age or Dragon's Dogma, I think it would be great to play on their side as they try to take over from the Argonians, Bosmer or even the Dunmer (and possibly even the Empire!) (not sure if anyone could really take of Elswyr) again.
Can you imagine playing a high level member of the Thalmor or Dominion cadres and having to change your whole belief system as you explore and learn about all of these different people that you have always been told on the Isles are inferior and need to be subjugated? (well, with the exception of the humans - they do indeed need to be brought to heel). I think it would be epic. But then again, I'm pretty weird.
While they are very interesting, I feel they (2nd Aldmeri Dominion) are to firmly established as villains. Unlike the Imperial and Stormcloaks almost all the Thalmor you meet are simply not nice people. That being said you meet a relatively normal person among their SS (Yes, I know.) in Markarth. They are good as part of the world, but not as a focus. At least to me.
So overall I do agree that if we could get more details about them it would be interesting, but still The Empire prevails.
Oh! I absolutely agree. Not nice in general. But, then again, they aren't evil in their own eyes. Villains to the other folks maybe, but not to themselves. They are doing what they think is the right thing to do (think the Emperor in Star Wars).
I'm a big one for moral dilemmas, particularly when gaming. An example would be just last night while I'm playing Dragon Age II. Do I go where morally I should given my character creation or do I go where my heart tells me to go (again as the character). I know that either way the end result is the same, but, I actually was so conflicted, I couldn't make the decision for almost 20 minutes until my other 1/2 said. Just do what you think she (my character) would do if you were her in real life. My decision was made and I had to accept the consequences.
That's one thing I love and loathe about SR at the same time. In RP, my decisions have weight. In the game itself, it really doesn't matter since nothing you do has any real consequences. I wish they would have added that aspect.