In both series protagonists solve criminal cases - one per episode or one per couple of episodes. Both have a main, leading story from past as well. Both have a romance with characters who are supportive towards each other and heal their old wounds.

In both there no love triangle or at least a very, very minor one, which doesn't really break anything.

Well, both shows about love through music with a dude being a musical genius and a girl having natural talent and a pure, honest heart. Both have a satisfying happy ending but with The Liar... you need to watch the after-credits scene. The Cantabile ML is totally different in character, funny, strong and sarcastic as hell, here we've got a more melancholic and supporting dude. Don't get me wrong - the Cantabile Chiaki-dude is supporting but in a different way and his mask agenda seems rude but in a funny way, you can't dislike his duo with Noda because their characters fit each other perfectly in such a romance-comedy. Try it.