First off, there is nothing original about Fairy Tail. The author just takes concepts and ideas from other battle shounen manga and rehashes them in Fairy Tail in a dumber way. Of course, to hide this thing, he also adds a lot of fanservice. So, whenever there isn't a fight going on, Fairy Tail will look pretty much like your average softcore porn cartoon. The story of Fairy Tail is fairly simple: the main protagonists go somewhere, encounter a villain who initially beats them up, then Natsu gains a power-up and wins. Repeat this formula endlessly and there you go, you have created a successful way of milking the cash cow. Of course, other battle shounen anime use the same formula too, but at least they make the story flow better.
Another flaw of Fairy Tail is the lack of characterization. Simply put, the characters are not interesting enough. Most of them lack depth or personality, especially the females, whose personality flaws are compensated with giant breasts.
The good parts of this anime are its art and soundtrack. I have nothing against them. The fight scenes themselves are good, so is the color palette and the music.
So, overall, Fairy Tail is a very generic battle shounen that doesn't try to break the mold: it present the usual tropes found in other anime & manga of the same genre while adding some excessive fanservice.
