I had to get used to the address bar but yeah, it's really great. One thing that annoys me (as with any version change) is that a lot of my extensions don't work. I bypassed the version checking and some stuff (like gears) still won't work. It all comes with time I guess :)
A thing that's really nice on the Mac build is that it looks like a native mac. It used to look like a Windows/agnostic window and never really fit in (and was made fun of by the other apps). But good to see the firefox team making this happen!