I picked up a reproduction cart of Super Mario Bros 3mix at MAGFest last year. Imagine taking the Mario series ranging from SMB1 all the way through Galaxy, tossing it into a blender, and running it through a Mario 3 filter and you'd pretty much get this game. Lots of added features and power ups, and there are a few "whoa, it's really cool to see this in a Mario 3 hack" moments. There are a couple moments where it lacks the polish of an official mario game but i'd be lying if I said I didn't enjoy the game a lot.
random gameplay video that I haven't actually watched: