* I've always disliked conversation view, and I keep ending up turning it off whenever I try it
* The lack of ability to sort emails is really annoying
* The layout of emails, particularly when trying to reply to an email, I find confusing - in particular it would make far more sense to have the text box at the top of the page
That being said, I probably dislike it less now than when I first started using it so I think the changes have generally been positive.
On a side note, I think Photoshop is also a UI disaster area.