Oh boy, where to begin on this review...
Story: Basically it's another "Magical Girl" anime plot, a girl who has the ability to transform must fight this evil group of villains with her friends/comrades as a Super Sentai team. The unique part of this anime is that the Mermaids don't attack, they SING, and their songs are painful to the villains' ears. Other than that, it's all cheesy.
Art: This depends on how you look at it. To me, the dresses for Lucia, Hanon, and Rina are full of many colors! (Practically every shade of pink, aqua, and green respectively.) On the other hand, the characters' appearances
are okay, except it's too overdone. (I.e. Doumoto Kaito with the most repetitive hairstyle of any Bishounen.)
Sound: What I found unusual was that Lucia's voice is different compared to other Magical Girl heroines. While their voices are high-pitched, Lucia's is lower, unless you count her screaming. Hanon and Rina sound okay. The MMPPP songs can really get to you, even though they're all about love.
Character: This is what bugs me. Basically, the Mermaids' objective is to unite the Seven Mermaid Princesses in order to defeat the enemy. The problem is, for 52 episodes straight, ONLY LUCIA, HANON, AND RINA APPEAR THROUGHOUT THE WHOLE SEASON!! What about the other four? Well, Caren appears halfway through the season, but she distances herself from them. Noel and Coco were captured so they're stuck with the enemy until the finale. And Sara is a good guy turned bad. Wow. (Did they expect girls to love the main trio more than the four Mermaids in the back?)
Enjoyment: IT WILL GET ANNOYING. At some point, you'll realize that there's too many fillers. Luckily, Wikipedia has already identified the episodes important to the storyline so you can figure it out from there.
Overall: Obviously the ending was anticipated. When the last episode first aired, it was already confirmed that a second season, Pure, would be in the works. (Personally I liked Pure more than this season.) It was an okay anime, it did introduce me to all the beautiful songs in MMPPP. Still, there were obvious flaws that could've been fixed.