I am a watcher of many animes, and the way I can tell how good or entertaining a series is is how it captures me in the first few episodes. Fairy Tail manages to do exactly that. Sure there are going to be a few weak points and continuity within the story, but there are plenty of strong points too. A good and bad note for the series is how there are so many characters within; it can be good because some characters you'll connect with better then others, but that is also a bad thing since it divides much needed attention to what is relevant at the moment, however Hiro Mashima handles it quite well. The score, done by Yasuharu Takanashi, does well in delivery the tones from intense to sad to flat out silly (and in many ways, saves the show in its weak moments).
Yes there are fillers, but not as many as other ongoing Shounen series such as Naruto or One Piece, and Fairy Tail moves at a quicker pace then both and the fillers for the most part are stand alone episodes in which the animators and studio story writers have a ball doing. The humor is very silly and childish, which is actually a plus I think.
It's definitely not the best series out there, but it has a lot of potential. It is a good solid series that I strongly recommend.
