This is sort of surprisingly not bad.
The individual mysteries are very formulaic, in a sort of Lupin III / Murder She Wrote / Scooby Doo sense - the recurring characters assemble through some extraordinary coincidences, a murder happens, they all stumble around seemingly uselessly, then the hero solves the murder It just has the added twist that somewhere along the way, Sakuya - the hero - is going to be killed. But that's okay because he's something resembling immortal and always revives, with his head on the lap of his long-suffering, fiercely loyal and charmingly tsundere assistant, Lilithea.
It has hints of harem, at least insofar as Sakuya has an ever-growing set of cute female admirers, but he only has eyes for Lilithea.
And the nuts and bolts of everything - the art and character designs and music and voice acting and so on - are all fine, if not exceptional.
So just on the surface, it's a passable, satisfyingly formulaic diversion.
But there's something going on in the background too - an overarching story of ridiculously gigantic proportions. It's playing out sort of somewhere between Full Metal Panic and Kill la Kill. And it might just be pretty good. Orcat least sort of surprisingly not bad.