We found it quite enjoyable. We did standby and stood in line for less than many FP folks who queued to get "good" seats. We were the first row behind the FP section and they let us in just a couple of minutes after the FP line started entering.
My daughter and I waited 20 minutes or so as she played with her souvenir stamp set and then it was an additional 5-10 minutes more after they had us cross the pathway to get by the entrance door.
The show is a FF of the movie with many of the musical numbers shown straight from the movie as sing along and 2 characters doing comic bits in between narrating the story.
Anna appears at the beginning and both Anna and Elsa appear towards the end.
It seemed many in the theater enjoyed the show. Especially the singing. I found that they did a good job having the narrators appeal to kids with silly puns and jokes that would amuse adults. I would totally see it again. Not sure if I would do it over and over again--but I am the same way about Fantasmic and Beauty and the Beats and most shows. I'm good with once or twice.
So I do think it is worth seeing once. Other members on our group saw it as well and enjoyed it.
Personally, I don't think it needs a FP+ unless you have a diehard fan who must see it above all else. SB should work just fine. FP+ is better used on the rides, IMHO.
But keep in mind, I saw this with my 4yo and my friend saw it with her 11 and 9yo, all girls who love Frozen. So, YMMV.