From an adult perspective, it's really meh. The animation and voice acting is lacking and the story feels so forced throughout the majority of the show. In the original h2o, the trio did a way better job of trying to hide their identities and powers, but the girl in this one act like they don't even care if their exposed. However, it's still cute and fun. From the other things my daughter likes to watch, it's a nice and entertaining change.
From my daughter's perspective, it's a really fun and quirky show. It's got all the ingredients to keep kids entertained; mermaids, talking animals, and magical powers. Excellent show to put on for your kids while you have things to do.
In all honesty, it doesn't even compared to the original h2o, which I absolutely loved. But it's good for kids.