Starts off great, but hits a stall in the middle, then devolves into shounen trope-y action and drama that's not nearly as well done as the comedy earlier. And the comedy itself basically disappears almost completely. It feels like the author used up all his good ideas in the beginning and middle, and then tried to tread water until he decided to finish with a predictable "all hands on deck" big boss fight.
Thankfully, the good half of the series got turned into the Anime. If you haven't seen the anime, I recommend it over the manga, although I will admit that the manga is good, is readable to the end (although it loses steam over time) and the art is very good. The artist engages a lot with his readers and acknowledges them and their fanart and original creations, many of which actually get integrated into the manga itself. Nice touch on his and Jump Square's part.
All this said, I still recommend giving this manga a try, and also checking out the Anime too.