I've played many extensively, but the most extensive by far was Wario Land 4. I was obsessed with that game as a kid, and after being disappointed with Wario: Master of Disguise a few years later, I went back to Wario Land 4, and I was still amazed by it!
Been also playing the WarioWare games I have extensively. Good thing WarioWare: Touched doesn't require the A button most of the time, otherwise I would have been bummed since my 3DS's A button is now pretty much shot, and I don't know where the charger for my old DS is.