For me, it was poor. Better than Campbell's run, but just as bad as Waltz's run after #50.(especially The Armageddon Game)
I am not excited about the turtles being together again because I tired of it. It feels like IDW keeps repeating the same things every time they switch writers. Leo and Mikey acted like hot-headed and angry one just like Raph, and had almost no personalities of their own. Hale is just boring villain, a filler character. Karai's plot only started to progress a little in issue #12. I don't know if IDW has a clear plan for this storyline. It's feel like the writer just set up a foreshadowing and then irresponsibly handed off to the next writer.
About Karai in this storyline:
She tried to open a portal to underworld but failed. However, she accident resurrected Splinter and maybe even controlled him. The new villain in Issue #13 might be Splinter because the name called Ujigami mean clan deity/divinity/spirit in japanese.