Although I don't post often on any forum I definitely wanted to share my opinions on how my experience went with the Smash Fest demo. I attended both the Wednesday, and Saturday sessions. I don't know if it was just the Best Buy I went to, or I just got lucky, but I had a total of 12 sessions on the Wii U (with three of them consisting of two 2:00 games), and around 18 go's with the 3DS. I spent all but two games working on trying out Rosalina and seeing how good of a feel I could get with her. Where to start though..
I can easily say I'm pleased with how she plays, and as mentioned above there's definitely going to be a very high learning curve with her, and perfecting the Luma Shot which will probably be one of (if not the most) versatile neutral-B's in the game. The Luma Shot is simply fun to use, and experiment with. It definitely has KO potential when fully charged which really was a pleasing surprise. I probably nabbed around 7 ko's throughout the entire Fest using just that alone. Obviously the ability to edge guard because of Luma is phenom, and creates additional hazards that your opponent has to be weary of when attempting to recover. There will also definitely be potential for some very impressive juggles using the Luma Shot due to the spacing you can create between the two if timed correctly. There were a couple of instances where Luma had fallen underneath Battlefield, and I had to take the time to jump off the stage and use my neutral-B again to call her up to me, but other than that I always felt pretty confident when I was using Rosalina in the multiplayer environment due to the separation I was able to create between the two. I felt like I was simply dominating the ground game.
In regard to force-summoning another Luma using her neutral-B after you lose one I was unable to do so. Her neutral-B, and side-B became essentially worthless when I was flying solo, although it didn't take too long before another Luma respawned by itself, so I was never in too bad of a pickle there.
Rosalina also feels like she can play very well without Luma. Of course there's more you can do when they're together, but I never felt like I was playing a single Ice Climber and was severely hindered or anything along those lines. I just wasn't able to rack up damage as quickly, and I couldn't create the spacing I would have liked to.
All of her smash attacks hit pretty well, and in conjunction with Luma I was definitely dealing sufficient damage quickly. They all had KO potential, and the start-up for all of them seemed very appropriate, and weren't hindering me.
Aerial game was definitely pretty solid, although I was pretty disappointed with the ko potential all of the moves offered. The d-air spike seemed to be the most effective, but the sweet spot is relatively small.
I definitely never died too quickly with her. She has a good weight to her despite being floaty. I'm pretty sure the highest percentage I got to before dying was 214% which I was pretty impressed with since I was getting plenty of kills throughout every match. Happily had 7 ko's with 1 fall in my best outing.
I spent most of my time quickly trying to learn the ropes with Rosalina, and devoted most of my play to quickly being able to use the Luma Shot, and just the two in conjunction with one another. I really didn't analyze her moves as much I wished I could have looking back, but I do know that her mechanics are just ridiculously fun, and I can't wait to lab with her as much as possible once the 3DS title releases.