Before I start I must warn you, that this review is written, with an assumption that reader watched previous 2 seaons. I won't hesitate with major spoilers of the preceeding shows, so if you haven't seen them then you might reconsider further reading.
Even the greatest can make a blunder, and past glory won't save them from it. A succesful brand with large fanbase. A 2 seasons, that receive positive feedback. J.C.Staff - company, that could be nicknamed "god of awesome cliche stories", for it's skills in making the unoriginal content shine. Sounds like ingredients for something epic? Unfortunately, the result is a bastard child of "excessive fanservice" and "annoying characters" - a one of a kind, total failure.
Story - 3/10
First two seasons of Zero no Tsukaima, weren't anything deep or extraordinary and no one expected them to be like that. They managed to bring out their charms, due to combination of cute, tsundere romance and magical world that resembled XVIIth century France. Among the fights, fanservice driven misunderstandings and arguements about the difference between nobleman and commoners, Saito and Louise slowly progressed their romance. That's why when the season 2 had it's epic ending I had my hopes really high up. I mean they married, god damn it. It should no longer be master-familiar relationship, but something deeper and more intimate...Unfortunately J.C.Staff thought otherwise...
Excessive fanservice won against cute relationship, and Saito x Louise are pretty much back to square one. Louise still acts high and mighty.You would thought, that having her go through the pain of loosing the loved one would make her mature up a little, but no, she is the same spoiled brat. Saito still can't manage to say no to the charms of woman body, which makes his self-declared love towards Louise highly questionable. The problem is - while this pattern worked when they were at "have a crush at each other, but not an official relationship yet", it's incredibly pathetic at "lovers, who vowed to each other" stage. If that wasn't enough, the creators decided to turn this poor show into pathetic harem. What previously was only a love-triangle between Saito, Louise and Siesta, suddenly changed into "almost every girl have hots for Saito". Tabitha does. Henrietta does. Tiffania, with her overgrown rack, also does. So we are showered with every female available having some ecchi scene, possibly with Saito. Great. The army of boys at their puberty might find this enjoyable, everyone else will yawn from boredom.
The story could still try to somehow defend itself, by delivering interesting bits at "fights, void magic and war" part of storyline. Unfortunately, this part naturally self-destructs, leaving the viewer with the question - what the hell it was about? First half of the show makes us believe, that Louise being a void mage (and possibly Tiffania as well) bears a great significance to the whole world. The evil boss sends his lackeys after her, to amplify the suspense. While the plot dissolves in the boring episodes, made only for fanservice, we can still claim to the belief that there is an evil force after Louise - so there is some story. Unfortunately after ep 7, the focus of the anime shifts completely. No longer any1 care about aquiring void mages - Tabitha becomes more important. They recall that they were after Louise, at the last episode, but at this point I didn't care anymore. The final battle, comes out bleak and boring, especially with the images from the previous season finale, of "Saito vs whole army", still burned into a memory.
Animation - 7.5/10
At least at this part J.C.Staff didn't dissapoint. The animation is crisp clear, and the fights, while not really breathtaking, are done properly. I could say something about ridicolous hair colours, but since it didn't annoy me that much during previous seasons (since the story was good) I'll stay quiet. However I have to take a note of ridicolously large breasts, Tiffania posseses. Even if I forget about how they defy law of physics - they are simply not appealing. Maybe there are people who have fetish for Eiken-like size of womans chest, but I don't.
Sound - 8/10
J.C.Staff as always hired amazing crew of voice actors, making japaneese dialogues very appealing for the ears. Stars like Rie Kugimiya, Ayako Kawasumi or Yui Horie are awesome spice to any show. With their easily recognisable voices, and a talent at bringing out character emotions, they are one of the few awesome things in this anime. Opening and ending weren't really good enough, to listen to them outside of the show, but I still didn't skip them so I'd say they are at average quality. Finally background tracks - they were appealing and tried to help set up the mood (even though the story/characters were constantly destroying it), but they weren't anything extraordinary. Just properly done music.
Characters - 3/10
I can forgive lack of growth from characters in shounen romance. But when they regress, and turn into annoying versions of their former selves, than I see them as a major failures. Like I mentioned before, Louise didn't learn a thing from the 2nd season. She still first smacks with a whip, then throw insults and finally perhaps listen a bit to what Saito has to say. This is already not a tsundere type - it's a bitch type. If you want to see properly done, loli-tsundere with Rie Kugimiya voice, go watch Toradora, since Taiga is the best use of that archetype I've seen in the anime. Saito still can't clearly say - "leave me alone god damn it, I have a partner already". Siesta instead of love rival, now plays the role of annoying meddler. Basicly even the most enjoyable characters from previous seasons manage to become irritating and pointless. Also without spoiling much I'll say that one character, who shouldn't come back does so, insulting the past actions, and making them turn into a pointless joke.
Overall - 3.8/10
Zero no Tsukaima : Princesses no Rondo can be compared to a drunken woman, that just fell off the stairs. You watched her for some time and thought she was beatiful. But now she's lying in the mud, with her expensive dress dirtied, makeup messed up, teeth broken and arm bend the wrong way. She still sends you, what she thinks is a charming smile, trying to seduce you. The questions remains - are you drunk enough, to see her as beauty, or will you look at the reality before you? This show is a mistake, that should never happen. You can watch it on the account of previous seasons, but you will be dissapointed nevertheless. I know I was. So unless you are prepared to sit through 12 episodes of pointless and boring, just for the sake of knowing how the story continues after previous seasons, I suggest you stay away from this show.