I think it's trying too hard to be close to the book. What mostly works in the book is the humour both in the (this is all hackneyed looking fun) bits and the natural humour that emerges. That, some miscasting, and full throttle on the over acting for effect at times.
On the other hand Only Murders In The Building works as TV and wouldn't work in any other format, it's a serial. I'd argue that the TMC would be better as a serial, probably 30 minutes an Episode. Then there'd be no excuse for the casting or the acting.
But then again it wouldn't get the same kind of budget, imagine it as Shakespeare and Hathaway, no shade on that but probably not the return that Osman might expect. A lot less than a pre-tea-time game show, I imagine.