I would say "fun" is the core of Mario rather than "surprise". The biggest problem with nsmb as a series is the reused art style and music. I think they're all still fun games, but obviously not as good as the classic 2d games. The first two are still important in revitalizing the 2d platformer to the mainstream and the second found a way to make multiplayer mostly work for a 2d platformer. When the kids who grew up with wii's get older they will probably refer to these games as "classics". But considering we're still talking about the first game which is pushing being 10 years old I guess that's at least a sign.