Asterisk concluded satisfactorily. They left an open end for another season if it happens to get made, and they wrapped up just about everything that led into and involved the Phoenix Festa, one particularly slimy student council president being the exception.
I thought the bit with Ayato's sister and Magnum Opus felt incredibly forced, and the fact that Ayato's sister was just chilling in a hospital in town and absolutely nobody in the hospital seemed to know who she was to alert Ayato comes across as a super weak and poorly thought out plot point.
That aside, no real complaints. It was pretty average overall, but I would watch another season if it was made.