It's hard to know where to begin with Zero no Tsukaima: whether to start by gutting the laughable excuse for a plot, perhaps castigating the clockwork collection of characters, or perhaps even starting on the atrociously simplistic animation and aesthetics. From all of this one could be certain that it is a show without merit, and while critically that is true, there are several aspects which I'm sure could make this a guilty pleasure for a select few.
Based off a series of light novels by the same author as "Green Green", Noboru Yamaguchi, and produced by JC Staff, the series has penalties before it even begins. The first episode does nothing to allay these worries and produces cliché after cliché in both characters and plot. The protagonist is a failing mage called Louise who summons an affable idiot from modern day Japan into Tristein Magic Academy; already it is fighting against other "fish out of water" anime and the obvious inspiration from Harry Potter. The rest of the series carries on regardless and stumbles through hackneyed and quickly ignored plot points and culminates in a poorly orchestrated and wholly expected "battle" intermingled with predictable character hook-ups.
Zero no Tsukaima fails primarily because it does not achieve any of what it promises: it is not funny enough to allow one to accept its flaws and not fan-service heavy enough to be able to switch one's brain off, its story is uninspiring even given such a vast canvas to work with and is so primitively drawn and animated in places it's hard to suspend belief. Louise is a painfully typical tsundere character who is (of course) soft-focus for Saito who manages to befriend every moderately busty girl in a hundred mile area; all the while the subtext of Louise being a void mage (obvious from the first mention of the enigmatic fifth magical element) and the uncomfortable idea that Saito is a bona-fide slave is prevalent. It feels like the series is belittling its audience rather than entertaining or engaging with them.
This is highlighted by the number of "oh who's that" set-ups which would try the patience of a five year old; or the number of secondary character defections which would be twists if it wasn't blindingly obvious from their introduction; or the alarming regularity at which seemingly uninvolved characters turn up on supposedly secret outings. These are just a selection of ways in which Zero no Tsukaima can make you feel like an idiot for continuing to watch it.
Given all this criticism then, the main redeeming feature of the series is the raw energy it rides upon; the speed and veracity at which it moves is a blessing. From the frequent subjugation of Saito by the boisterous Louise to Saito's continual misinterpretation of situations, it's hard not to be at least slightly endeared by the colourful figures running jerkily across the screen. Empathy is hard to come by when so little of the characters' histories are explored, Tabitha is the exception to this and manages to convey confidence and inner-pain long before her past is extolled.
Unfortunately these are perhaps symptoms of searching for something more from a series which offers so little; Zero no Tsukaima continually falls beneath any expectations of competence and could perhaps only offer solace to those waiting for the next scrap of sporadic fan-service or for those with the mistaken belief that it can only get better as it progresses. Enjoyment could only be wrung from the contrast of low-maintenance, slapstick situations and high-fantasy setting.