I've got to give Yahtzee credit here. Mario and Luigi: Fantastic Voyage is basically exactly what you'd expect---a lighthearted, fun little romp that you don't have to worry your pretty little head about, the perfect break if you've been playing, say, Oblivion with FCOM and a host of other mods installed and the difficulty slider all the way to the right and want to feel like you don't totally suck at games.
It's the perfect game for a system like the DS, where you're most of the time going to be playing it in the sorts of places where it's really hard to get a rhythm going (unless you're like me and just play it in bed.) Nintendo knew exactly what it was trying to do, then they went out and did it, which means Yahtzee is left in a position where he's got to venture off on constant tangents like the sublime commentary on Gilded Age sociology that is the Mushroom Kingdom.