- Email threads ("Conversations?") look like Facebook. You've already done that once.
- In a case where there are several areas filled with text on the screen, and one does want to pack as much text as practical onto the screen, I like boxes around things, not just horizontal lines between them. It's easier for my eyes to stay focused on what I'm reading. See, for a good example, the NYT's home page. This applies to both the particular conversations and the lists of messages, as in the Inbox.
- The icons on the new toolbar take longer to recognize than the old toolbar's text-labeled buttons. Out of the corner of my eye, so to speak, they're just gray blobs. I actually have to stop and look at them, if you know what I mean. And despite their apparent minimalism, the toolbar takes up more space. More on the new toolbar.
- I don't like the way the "folders" (Labels) list expands and contracts in response to my mouse hovering over it. Just leave it static, and let me decided to expand it with a click. I've chosen which items to display in the list, again, so to speak, so I can see the things I want out of the corner of my eye.
- The shades of gray color scheme wouldn't be so bad if the ads in the right column weren't filled with bright blue text. I mean, I know you're offering a free webmail service as a way to get me to look at ads, but come on. Yes, I'm aware there are themes available to change the look. None of them addresses this problem satisfactorily (although I have to admit, the Planet theme is pretty cool). How about a theme that makes things look like the soon-to-be old Gmail look?
I grant that some of these things are in the category of Dumb User Dislikes New Things Instinctively And Will Soon Get Used To, but still, you asked. I don't see what the new design buys me, even if I imagine getting used to it. I can't see that I'll be getting anything new out of it, so why force what appears to be nothing but, literally, a new look upon me?