Zero no Tsukaima is based of the novels of the same name written by Noboru Yamaguchi. They detail the adventures of Saito Hiraga in a land ruled by magic called Halkeginia after being summoned there by the mage Louise. Louise, a student at a prestigious Tristain Academy of Magic, who causes devastation whenever she tries to perform which earns her the nickname "Zero." In her attempt to summon a familiar she summons the normal 14 year old boy named Saito and he must deal with being away from earth while adjusting to becoming the hot-headed Louise's familiar.
Zero no Tsukaima establishes a great plot which, unfortunately, degrades over the course of the series for harem antics. The plot establishes itself as we deal with the problems with the magic academy which give it a Harry Potter vibe. However it eventually branches out to include other countries and eventually the threat of war. The series really shines when it establishes the world around it which is similar to medieval earth. The hierarchy system in which people who cannot use magic are put at the bottom and those who can are given titles and leadership is a realistic view on the bias that would probably be seen in such a society. Saito as the familiar gandalfr has an awesome power: he instantly knows how to use any weapon upon touching it. He also gets strength and speed buffs.
So how does such a good plot setup fail so hard? It starts delving into cliches and focusing on the harem aspect while practically ignoring the plot. the characters, while being cliche' at first delve further and further into cliche'. Louise stays in the 'tsun' part of 'tsundere' so long it gets extremely tiring. Most of the characters share this fault: they don't grow on you, they actually get more annoying as the series goes on. Siesta the maid is simply there for fanservice and Guiche and Montmorency are there to foil the relationship between Louise and Saito. The overarching plot gets all but forgotten in the last few episodes exchanged for how pretty much all the girls want Saito. I understand that this has something to do with self gratification, but there are dating sims and other shows for that, why abandon a decent plot set up?
In the end I really wouldn't recommend this series for those who want plot to go with their fanservice because it really just degrades into fanservice with little mention of the plot and by the time it is mentioned again it gets rather hard to follow and that's due to the bad adaption of the series. The novels, while also having fanservice moments, have a far better established plot. I will admit that the series was doomed from the start since they cover 3-4 novels in the first season, but the have at least one episode which is completely original for an underwhelming joke a waste of 25 minutes. I have no choice to give this series 2/5 because the series discards a rather intriguing plot and without that the characters show how dull they are.