Fairy tail is your average battle shonen. Its problem is that after a while its gets painfully boring. All the arcs are the same:
1) new OP enemies appear
2) Main cast is unable to face them
3) Deus ex machina/old enemy turned friend appears/Power up based on power of friendship appears
4) Victory until the next (identical arc>)

I know this is the main formula for all battle shonen manga but Hiro Mashima does nothing to mask it and keep the interest high.
On the character's side, the initial design is interesting, but there is almost no evolution or growth at all for the main cast and even when you think there is some change, then you see the very same character who should have been changed acting exactly like he did at the start.
All in all, as a no-brainer action work, it does its job but it pales in comparison to other manga.