I love the manga, it's one of my favourites out there, but I thought it could've been so much more. It's not that the characters are shallow, the arcs short or anything like that, but it's like the characters could be deeper, and the arcs could be longer. Don't get me wrong, I love this to bits, but it kills me to read it thinking about everything that it could've been. The arcs are short enough so you don't loose interest, yes, but the development on the characters in them lacks. For example, if someone shows up for an arc, they remain a small crappy layer unless they are reintroduced, and even then, that does very little unless they become one of the main group.
Then there's the battles. The main characters don't seem to get stronger, not even miraculously so for the final fight, but their enemies just get weaker the second time around. Lucy is so blatant with this. And what annoys me the most is that between arcs the characters get hugely stronger even though there is only supposed to be days, maybe a week or so, between each arc. I mean, seriously! There's no training (bar very later chapters), and the main strength comes from nakama speeches, which are utter bull. Then there's the fan service. About 1 in 10 women in it are normal, the rest all big breasted and practically whore about. It's like a constant summer where all cloths bar bikinis and other revealing things don't exist. I mean, poor Levy who's normal, but looks not as good do paired to the others!
Yet, you can't help but read. There's no real sustainable plot after the Tower of Heaven, maybe the Edolas arc (but that might just not be), and things appear as if from nowhere without explanation other than "you were gone and they somehow conveniently did this and this happened". There's no real motive to finish, but you just do. It's good fun to read, even with all of its many, many flaws.