I, like Lil' Lori haven't done L.A. to Hawaii (yet--but very soon!) but I have been on Regal Princess several times and I love it.
Lori is right; it dosen't have as many venues and activities as Princess' larger ships--but it is by no means a "small ship".
It is very nicely appointed but not as "elegant" as the newer ships; which is fine with me because it gives it a little more relaxed ambiance.
But what I really like about it is its space. The cabins are much roomier, with more closet and storage space than the newer ships--ideal for longer cruises. And it has nice wide decks and large pools. The swim-up bar is a kick. And the pizza restaurant is great; it's sit-down, but near the pools, enclosed, and very casual with good views and checkered tablecloths--not to mention great pizza, salads, and other items.
My only complaint would be about the Dome. One side is the casino and the other side is observation lounge/coctail lounge/
entertainment venue. Problem is, the casino side allows smoking; and while the othe side is non-smoking, the smoke wafts over. This was not a problem for me as I don't use the casino and there are plenty of other places for drinks and good views--I only mention it in the spirit of full-disclosure.
I have never been on any other line than Princess so I can't make any comparisons; but I have sailed with Princess for over 30 years and never had anything but great experiences.
Diamond Princess will start the L.A.--Hawaii run in September if you are interested in a larger and newer ship. It is great too, in it's own way.
I hope this helps. If I can be of further assistance, please ask.