To be fair, the only problem with the series is perhaps a poor management of the story.
If you look at the staff, with how episodic the show was in mind, and compare it with the simple OVAs, you can see how the task of going from movies to a big series must have been overwhelming for the director and writer.
It's not like Michiru Shimada (who did most screenplays and series composition) doesn't have enough experience, but I wonder how good of an original writer she is. The second movie (which she wrote) was much weaker than the first.
Plus, juggling this episodic mess with a director, who before only focused on bombastic endings and simple one-episode fairs, must have been hard.
It was an experiment to see if Yoh Yoshinari can direct a long series. Unfortunately, the big story was fumbled a bit and felt like an unpolished last-minute thought, though it had such a great potential (and a lot of it was still great).
But that's just me assuming. I wish that an actual good journalist would dissect this.