Just downloaded the New Super Luigi U. A pretty good game although its a whole lot shorter than the Super Mario Bros U. Most levels have a fairly short time limit so its pretty easy to just play through in fairly short sessions.
From the gameplay so far you have somewhat less control, seem to skid a bit more before stopping (not sure if its just me). But other than that pretty awesome game/expansion.
Something noteworthy is Nabbit is pretty awesome since his pretty much invunerable. Means multiplayer is a bit more bearable since at least one team member is almost always garunteed to survive. However if someone who doesnt need his invunerablity is playing him, he is a massive prick. See below*
Highly recommend that you pick this game up if you have the cash around. Dont need much time to play each level is only takes a couple of minutes so its pretty awesome when you are busy.
*I have been banned from using Nabbits [the Dick] at my friends house, since I stole all the power ups all the time and therefore earning the character the above ammended name. But to be fair power ups give me a 1 up when I complete the level...Why wouldn't I want to take them all?