I just did it (g15 went to wife so still have both ). Both are really good point and shoot cameras but the G7XII is certainly much better.
Few things that I really like.
- Wider angle
- cleaner files, especially at higher ISO's, this alone makes it worth the upgrade.
- Flip out screen
- I love how you can bounce the flash. Seems almost silly that I like this but it's a nice feature.
- WIFI, I didn't think I would care but this is really a nice feature
- touch screen works well
- the control dial in front is very useful
What I don't like
- I prefer the feel of the G15. The G7XII is a bit too small but I guess small can have it's advantages.
- lack of a viewfinder - The G15 is bad here too but I really wish Canon had one like the Sony.