A quickly thrown together list of what changed, please expand as you find things that changed:
Overall
- The Logo (and site name) got larger
- The top bar got smaller and the horizontal links were moved to the left-nav
- Site section headings lost their bold, their teal color and got quite a bit larger
- Grey font colors were replaced with black across the board, except on tags (and the tags page)
- Links are now not only blue, but also underlined
Tags Page
- Not definitively sure, but the Tags page has slightly larger font?
Questions page
- Tagged QuestiionsQuestions page now includes the name of the tag
- Tag wiki and tabs ("info", "newest", ...) on Tagged questions "switched", Question counter moved to the main container.
- Because the switching sufficiently separates the tag excerpt, it's no longer in a box outline (also editing the tag wiki is linked from tagged questions)
- Responsive design is in effect.
- Voting buttons have been changed to the standard triangle instead of the angle in a circle
Users page
- Minor change in placement of search box and the design of the overall tabs.
- The Filtering box lost it'sits "Type to find users:"
- Profiles have a little less horizontal spacing between the left-bar and the main container
- The "accepted" color on the post pages in user's activity now matches the (darker and more saturated) reputation graph color (which didn't change).
- The Answers counter on the user's question details now gets a border when there's more than 0 answers instead of just a font-color change. (Also colors have been unified). (Also applies to favorites & reputation)
- The colors for the view counter seem slightly darker (which improves readability)
- The user actions (in activity) seem to have gotten changes as well:
- The "Accepted" marker for accepts is now dark background with white font, instead of light green background and dark green font
- the "comments" in activity are now with properly black font color (not only for bold) and a slight decrease in font-size
