After owning a G12 for a year, I replaced it with the G15. The G15 is a bit more refined and a little smaller. I do not miss the pivoting screen and I like that the flash is now concealed since I rarely use one.
The PowerShot G15 is a successor to the popular G12 and is built around a 12MP, 1/1.7" CMOS sensor. Its lens also gets an upgrade - retaining its 28-140mm range but now with a maximum aperture of F1.8-2.8. It loses the G12's articulated screen but gains a higher-resolution, 920k dot panel.