Well I liked the first four cases of PW and played through it one after another, but I guess then I got kinda bored. Especially with that fifth cases, some of the NPC's were just annoying the shit out of me (that cowboy policeguy for example) and it was like three cases intertwined with each other. Got a bit too confusing to be enjoyable for me.
Haven't started on the sequels yet though, I plan to try those in a while.
Certainly nice games, that require a bit of thinking. But like almost any game (save for Cross and perhaps Trigger) after playing it days it just gets a little boring.