One thing I dislike in the new Google styling is the general lack of contrast. It makes navigation a bit slower due to delayed object recognization for power users.
Everything just takes milliseconds longer to sink in.
This is my biggest complaint as well. The new features of the UI are great, but it still looks pretty bad. There's a lot of white space and very little contrast between elements are groups of elements. The "Compose Mail" but just sort of hangs there awkwardly. The top row of action buttons are aligned to the left, so at higher resolutions there's just a chunk of whitespace to their right, even though the inbox itself fills the entire width of the container.
On a related note, I find it very difficult to distinguish between the white background of unread message rows from the very-slightly gray background of read rows. (Probably worth noting that I'm mildly colorblind though.)
The bold subject on unread messages helps, but it isn't enough for my eyes.
1) using the page space for fixed "app-like" UI instead of just presenting the page. UI on top of UI really doesn't make using their pages better for me. The scroll bars get smaller, the effective vertical space of my screen usable for content goes away exactly at time the screens on notebooks get always less vertical pixels. Things go horribly wrong recently. Compare 1973:
I don't understand using red to mean something other than "stop" or "cancel" either.
It reminds me of the first time I tried to use a cell phone: I didn't own one and had borrowed one for a trip. I could not figure out how to turn it on. I kept pressing the green "TALK" button and nothing happened. I assumed the battery had died. Turns out I was supposed to press the red button labeled "END" which is the last button I would think to press.
At the same time, I find it to be a lot easier on the eyes. As a "power user" spending a lot of my day staring at my inbox, I like this a lot better. Pretty soon all of the buttons will be second-nature anyway.