About the Camera and Gallery improvement in 4.3, maybe you can find something interesting in my reviews.
Photo editor improvement:
Better pic quality,
New editor UI,
faster but more heat.
Take photo by volume key,
New arc menu,
New shot animations,
Autofocus speed up(not sure)
Actually, the Gallery app might have been updated to the 4.3 version automatically in stock Android 4.2, reported by some people, it is the same app as the 4.3's.
BTW, people who are using 4.2 and want to try the new 4.3 gallery and camera can download the apk directly, you should intall the gallery.apk. if you copy and paste it by root explore you might get photo editor keep FC,
(at least I met such problem.)
One bug: camera autofocus status freezed if you keep touching the screen while you didn't move the phone. maybe the new baseband will fix this issue.
Nexus 4: CM10.1 + Faux kernel | Xperia S: OpenSEMC
[retired]Milestone : CM9 | Xperia X8 : kuyaDROID v3