If you're looking for mainstream things where the characters level up by training and stuffs and starts to become stronger like in Naruto or Bleach, this anime won't live up to your expectation. You'll just be irritated on why the enemies are too strong for them.
I was expecting something similar to that when I started watching D.gray-man, as it is a popular anime but I guess I was off the mark. If anything, D.gray-man focuses more on developing its story rather than its fight. However, it wasn't really executed well imo and did gave me a let down.
The fights were..horrid. They will fight without any improvement and keep getting beaten up by the enemies. Even when they get a power up, the enemies that appear will somehow be more stronger than them and then they get beaten up again.
Overall I give a 7, just for the sole reason of the story being good enough to follow although it is still executed poorly. The character development was good enough though, because they explored more on the story they have more room to do it.
