Played the demo completely. I like how it starts with the seesaw mechanic, which I don't recall in previous games. The drill is cool. I like how I can skip most tutorials with the press of X or Y, but that seems to be a demo thing.
Action commands seem a lot easier to do in this game. I've been getting excellent on the hammer and jump attacks 95% of the time.
Luiginary and Bros attacks are more flashy than the previous iterations' counterpart. Gonna have to get used to gyro however.
And it also seems Mario & Luigi are quite powerful in this one, especially with the special attacks. That skateboard one did ~95 damage to one of the bosses you can face in the demo (Grobot was his name I think). But even with the high damage, it didn't die quickly. Basic attacks start with ~20 damage if you manage to get Excellent on the action commands.
Dream sections are like the 2D sections of BiS, but I only played a short part of it. It seems they will require one to use Luigi's abilities a lot. The demo had the mustache-pulling, and the stack. The stack seems like it will be used often.
I was getting my butt kicked by Bowser though. Wasn't used to moving and dodging lol. Didn't die though, but was getting hurt a lot and had to heal.
I enjoyed the demo and left a positive impression on me.