I'm not so surprised they failed the ending too, I mean, after episode 4 the show showed all its limits. The story was predictable, the side characters looked like were chosen randomly and put here and there along the story. And, I didn't count them, but on 12 episodes, how many school festival did they organize?
Is this a sort of reverse advertising? something like ok, this is a hint of what the game is, we left you unsatisfied, now buy it to fill your emptiness!
Anyways the only thing I'm glad of is that they didn't give kiriha screentime at all, she looked a really cool character, (I don't know if she really was) so they hadn't time to ruin her too