I just went to the Nintendo E3 at Best Buy. Only an hour wait. Mario 3D World is a great 4 player game, but you can only try one level and one game. I also got to pick a flimsy foam Luigi hat as my prize. 
I went today too. After 30 minutes I was able to watch the demos of all 4 games (DK, Mario 3D, Mario Kart, and Wind Waker) and I was sold. Mario Land 3D is the best 3DS game hands down, cant wait to play more of the same.
I didn't get to play anything, because we signed up and the line wouldve been at least 90 minutes, though probably closer to 2 hours. The thing was poorly planned, with 1 demo station and playtimes of 10-12 minutes per game. The group playing Mario 3D finished their level and they said "you want to play another?" Doesnt make sense with a huge line...
However, I got 2 free Luigi 30th anniversary coins which are awesome, some Mario Kart flags, Luigi hats, and some Wii U booklets for free. There was also free coffee from the Kurig on display. Overall, can't complain too much... hope this happens again next year with maybe 2 to 4 displays at least.