A mouthwatering combo, to be sure. Something interesting about the resulting product: Muji adds another dimension to Lego. Of course, Lego is 3 dimensional and Muji doesn't add a 4th dimension, but they do add a layer of 2-D flatness that is not normally in the Lego world.
The resulting builds are certainly charming, but I must admit, all that paper cutting, template marking and tiny scissor work feels a little fussy. I'm screwy for Muji, make no mistake, but this doesn't feel completely true to the natural, intuitive quality of Lego.