In terms of plot, Kishi could have made many improvements to the story in order to make it more interesting. It seems like everything after the time skip is getting rushed because he's just introduced too many characters and there isn't enough time to cover them all. He can't flesh anyone out, there are just too many. Even the Dragonball manga didn't have this many characters, and Toriyama struggled with keeping those chars relevant, especially in the latter half of DB.

I guess my real complaint is that Kishi introduces a plot thread, or hints at something (ROOTS, like Assertn mentioned) and then just drops it for like 100 chapters. I also think he could have used the timeskip to really give us some background on the characters, or just show some nice snips of their training. At least more than 1 chapter's worth.

I don't have a problem with characters using the same techniques over and over, that's their specialty. Just because we've seen it before doesn't mean their enemies have - if it's effective, why not keep using it? Besides, as we know, it takes a long time to create a new jutsu and it's difficult to learn existing ones unless you have the affinity for that element.