I've only been on one Princess cruise and it was the smaller, Pacific Princess (former R3 ship). I DID do my homework before booking the Princess cruise though, but still was disappointed.
I think Princess is more casual than RCI. I didn't find the service on Princess to be what I expected either, but it was only one cruise.
Princess has some pretty great ports and lecturers though, if you're interested in this. Also, I'm not a buffet guy but due to some unfortunate happenings, only ate dinner in the specialty restaurants and buffet. The buffet was pretty good and it was the same menu as what was being served in the dining room. I thought that was a nice offering.
I enjoy the entertainment more on RCI and the dining as well. Specialty restaurants IMHO are better on RCI.
I was told by a regular Princess passenger that I should have tried one of the larger ships, as my experience on the Pacific was not indicative of their overall service. If you do try Princess, maybe try a larger ship?
If you like RCI, Celebrity may be another good alternative for you guys.