Jury is out on the new maps. The satellite images are newer than what is on Bing or Google though.
Siri is noticeably better than it was previously. I was able to ask “Where’s a good Pizza place around here?” and it got me a list. I asked it “Are there any new Bruce Willis movies out?” to which it found the Expendables and The Cold Light of Day and where they’re showing.
I haven’t noticed anything else. I saw Passbook (the new app) but can’t tell you if it does anything useful other than in theory.
The full change log can be found here.