I've been on four Carnival cruises. Two were one week and two were the three day weekend trips to Ensenada. The last one was a couple of weeks ago on the Paradise.
Nothing bad, but nothing great either. My one week cruise on the Pride to the Mexican Riviera is one of my two favorite cruises (a thirteen night cruise through the Panama Canal on the NCL Jade is the other). My opinion of the cruise on the Paradise is not much different than my opinion of the same cruise on the Holiday seven years ago. Again, everything was okay, but nothing great. The food was average (the food on the Pride and Glory was very good). The room steward was average (the room steward on the Pride was great!). The waiters on the Paradise were good (the waiters on the Pride were great).
Everyone did their job, but I got the feeling that for the staff it was, oh look, we are in Ensenada again. This ship does the same thing twice per week except it visits Catalina only once per week. The ship and staff did not seem to have a personality. It was like watching a good movie for the second time. It was good, but nothing stood out.
Is it worth it for a quick getaway? Yes. Would I substitute it for a longer cruise? No.
My review is mostly written, but not finished yet, so I can't provide a link to it yet.