This very different new theme and the window button changes don't seem to serve any purpose other than to make new visual changes for a new release.
Ubuntu might do better if they kept a better measure of consistency in the look-and-feel and user interface between versions.
For example, the shut down and log out buttons were separated in 9.10 and there is no longer any good way to have a single button that can simply shut down, standby, hibernate, and log out. There was no real need to change this and not provide a way of doing what was possible before.
Also, the volume control was merged into the notification area (to improve usability no doubt). The problem with this for me is when I watch a fullscreen something on my primary monitor, I cannot simply place a volume control applet on the other and scroll up and down to change the volume like I could before without making the primary notification area sit on the second monitor.
Change for the sake of change just doesn't seem like the way to promote a good Operating System. There will always be detractors, but Ubuntu should aim to have the level of consistency it needs for people to identify it (over a period of time longer than 6 months) as a particular brand.
Additionally, I personally would hate to see the old human theme disappear over time because a newer Macintosh-like theme takes some artist's fancy. I think the old human theme really captured the essence of the term "Ubuntu" (and the icons looked easier to associate with the tasks and didn't take so much space).