I am a big fan of the typical Japanese "Mys-Com", the Mystery/Investigation dramas filled with various degrees of similarly typical Japanese humor and comedy, but in all fairness the genre has produced many dramas better than this "Shinso wa Mimi no Naka", which was, for me, quite a let down.
The leads are OK, Tsutsui is cute as pie and Ihara pretty funny, but I honestly really disliked the supporting characters played by Nakamura and Morinaga, and that didn't help.
The script was just "meh", the mystery part not particularly interesting, and the comedy part not particularly funny; add that the last episodes switched to a gloomier, darker atmosphere, and you'll understand why this didn't really work. Forgettable.