I'm a huge mermaid fan so my opinion might be skewed...
I saw the show on January 6th and I took my mom, DF bought the tix for my B-day.
I enjoyed it to be honest, but I was not WOWED as I was when I saw Beauty & the Beast. I was extremely disappointed in costuming. I understand that they have to work with most major characters having to swim and not have legs, but to me it just looked like Ariel had two tails...it was especially weird when she sings Part of your World where her one tail is behind her and the other is in front.

And don't get me started on Flounder's costume!!!!
What I liked - the segue into Land to sea and back again, most of the time anyway... But I did think this was cool
I also liked most of the additional songs... But I liked Beyond My Wildest Dreams on the demo better, it was sung a little differently. I also kinda liked If Only on the demo too since it was just Ariel & Eric, but I did enjoy the quartet too but I think I prefer the duet.
I thought the actor who played Triton was Awesome!
I that Sierra Boggess did a pretty good job, out of all the Disney Princesses, IMO, Jodi benson's voice is most recognizable so she had a lot to live up to. I liked her, and I thought she captured Ariel's personality really well.
I liked all the additional scenes with Scuttle, I really like him as a character and loved that his part was bigger.
What I didn't like.... The actor who played Sebastion, it was just ok and honestly Sebastion kinda helped carry the movie. I just didn't think he was up to it...
Ursula... I thought she was too pretty and not 'scary' enough... I remember when I was like 10 and seeing TLM on Disney on Ice, the Ursula then was awesome and I was terrified! I also didn't like her additional songs at all. She didn't have enough sass for me.
The costumes.. I wasn't impressed, the double tails freaked me out.
It didn't add alot more jokes either, most of the jokes where from the movie but just in different areas of the script... I thought Beauty & the Beast added a lot more humor to it....
So as a Mermaid fan, I did enjoy it and would probably pay money again....but I just didn't think it was as spectular as Beauty & the Beast. It just wasn't as perfect as I thought it was going to be...but I did enjoy my 2.5 hours in the theater and so did my Mom.
I was also very disappointed in Lion King.... I love the original score, but didn't like the show. I saw it in Philly though so maybe because it was traveling it might have been different...
Hopefully that helps...