I had not heard of this series till I saw it on Funimation's site (and their YouTube channel) where it can be viewed legally on line. I was immediately impressed by the high quality of the animation and that even though there was a large cast the characters were fairly distinctive, so I could tell who was who even though I had difficulty remembering their names.
Negi is a ten year old Welsh wizard who is given the task of teaching at an all girl high school in Japan where he is in charge of class 3-A for the most part they are fairly ordinary girls, exceptions being that Evangeline is a vampire, Sayo is a ghost and Chachamaru is a robot. Much of the story takes place in a parallel magic world where the class has been taken by a strange item known as the "Star Crystal". In order to combat this Negi enters a contract with each class member which enables them to become his magical assistants. Unfortunately the series seemed to drag quite a bit in the middle and while I liked the characters of Negi and the girls I wasn't so keen on his talking pet ermine and two strange creatures which were apparently a frog and a cat which didn't really look like either and were rather annoying.
It seemed rather strange that he entered these contracts by kissing them... after all he is only ten. Apart from that the series was fairly free of fan service, there was some nudity in the transformation scenes as the girls magical contracts are activated but this is soft focus showing nothing. The same can't be said of the two OVAs which are almost nothing but fan service. This came as quite a shock after the innocence of the series, they were pretty funny though. Don't turn off when the end credits start as there are comedy shorts after they finish, some of these are one-offs, others like the "Baka Rangers" have several episodes.
I guess this wasn't the series for me although I wouldn't advise others to avoid it, especially as it can be watched legally for free on line, give it a go you might like it more than me. As I haven't seen the original version I can't say how this compares.
These comments are based on watching the series in Japanese with English subtitles.