Maken-Ki! is a great example of 'Don't judged a book by its cover.'
Harem type animes are usually all the same and that pretty much drives people to stay away from any new ones that air. I personally feel the same way, though when a friend who does not like anime recommended Maken-Ki! to me I thought I should check it out.
Lets get down to the review starting with the basics.
Maken-Ki! has an amazing art style, and the voice actors were chosen to fit there rolls perfectly.
However thats all I can really appreciate about the anime. Big boobs, perverted teenage boys, 4+ girls fighting over a less than average male who has a jealous friend who does not get any action, your typical Harem anime. I'm afraid that when it comes down to originality Maken-Ki! falls a bit into the shallow end of the kiddy pool. Though not all is grim, they make up for being unoriginal by adding a cluster of strange and random events that help build the story.
Maken-Ki! Takes place in a high school that has just changed over to coed. Takeru Ohyama transfers to this school with nothing but the thought of boobs and panties in mind so he has no idea what he is about to walk into. The school Ohyama joins is a special school where unique students hold mysterious and unique powers known as 'Maken' and they use that power to duel other Maken users over pointless things like who will have to be on cleaning duty. Takeru Ohyama joins the school's enforcing club, 'Maken-Ki' after being recommended to it by his childhood friend. Its the duty of Maken-Ki's members to stop unofficial fights around campus, because Ohyama does not know how to use Maken he gets himself into some quite interesting situations.
Maken-Ki!, like other harm animes is about 70% fan service, 20% story, and 10% character development. The anime really falls short on wow factor other than boobs defying the laws of physics. Personally I did not walk into Maken-Ki! with high expectations but the anime really was not that bad, because its so short it felt like I was able to sit through it while still enjoying myself at the same time. If someone asked me if Its worth watching I would say "Yeah, give it a shot." With a decent story, outstanding art, good character development and a fair enjoyment level I give Maken-Ki! a 7 out of 10