Overall the show is quite enjoyable, but it fails to leave a lasting impression. If you're looking for some light entertainment, give this one a go; contrary to what my final grade may imply, I can still recommend this one. Grading the show solely on the ability to make you smile, it would have received a solid 7/10. But it's earned itself some demerits in other areas. The main cause of its shortcomings seem to me to be the fact it tries to do too much, not giving itself enough time and space to actually do it right.
It's fun when it sticks to what it does best; lighthearted mysteries of the "let's hunt for ghosts"- and "who stole the apple-pie"-calibre, which the protagonists commit themselves wholeheartedly to solving. This contrast, and the contrast between the two main characters, produces a steady stream of low-key humour. Sure, the investigations always go suspiciously smoothly and they always manage to leap to the correct conclusion based on very limited data. But who cares? It's fun. It probably won't make you laugh out loud, but that's not its intention.
Unfortunately, in a lot of episodes it tries really, really hard (too hard) to be dramatic and touching, cramping the set-up, building of tension and resolution into a span of 20 minutes or less. With mixed results. Supposedly emotional breakthroughs are glossed over and profound issues are solved in laughably simplistic ways. Not to say they're all misses, but the success-ratio is rather low.
There's not a lot of opportunity for development and exposition of the main characters, but there's no real need for it either. Their chief function is to guide you through a small mystery each episode and entertain you in between, which they do successfully. The two main characters interact nicely together and each have some charming quirks and the humour flows naturally from their personalities. The supporting cast is a bit bland though (and not very supporting).
But little room is made for music. After the (perceived) promise made in the first scene, and having been directed to this show after finishing (the wonderful) Hibike! Euphonium, this realisation came as a bit of a let-down. In all fairness, this was largely caused by my own preconceptions, I can't actually hold against the show. So just take this as a friendly warning to spare you similar heartbreak; the premise of scrounging together a concert-band is little more than a framing device. It could have easily been replaced by, say, the formation of a volleyball team. There are one or two nice moments when the theme of music actually serves a purpose. So I do think, had it been more intertwined with the story and given more space, together with the whole let's-get-together-and-build-harmony-bla-bla-bla concept, the show would have been richer for it.
As a bonus; actually acceptable English! Just a few words, but still. What a relief! (A bit sad this should count as a cause for celebration. Sure, it seems Japanese are bad at English as a rule – a fact of which they're quite aware and a point of much appreciated self-ridicule – but if you're going to put gai-jin in your show, hire a suitable voice- actor or at least hire a consultant!)