I'm not sure what it is, but the new top bar just feels cramped.
The font is kind of thick, and that makes it look smaller. You're shoving more icons on there, half of which are more confusing than just a plain text label, so that's also more cramped.
The proportions just feel way wrong. The old bar felt a lot cleaner.
##End review: =(
End review: =(
FWIW, I also am way less likely to go to review now, because it's smudged off right, and I have to think about which icon it is, and ugh.
The fact that the Area51 and stackexchange.com top bars are not changed is going to make this even harder to get used to.