I'm an enormous Mario fan, and I think that they're milking that series - not because of how often the releases are, but because the games all look, play, and (musically) sound the goddamn same. All four of the NSMB share the exact same aesthetic designs, which can't be said of SMB, SMB2A, SMB3 and SMW. All of those games look, sound, and play immensely differently. They're milking the series because they're making numerous sequels that obviously required the bare minimum of creative effort.