I have weirdly specific memories of Riviera — I played the game for review back in 2005 and used it to while away an otherwise agonizing hour-long wait at a nearby Italian restaurant as they tried to figure out my take-out order. (Sautéed vegetables are apparently trickier than you’d think.)
Thankfully, Riviera was strikingly good. Not only did it kill that hour of hungry torture, it kept me entertained for another dozen hours or so after that. It also managed to completely overcome my misgivings about dating sims, graphical adventures, and many other things I normally dislike in my games. The trick, I think, is that Sting managed to incorporate all these elements into something that resembles an RPG and came up with something weird and unique and yet internally consistent from start to finish.
Phil did a bang-up job breaking down the specifics in his write-up for GSQ6, so you should read it and soak in the science.