I've been paddling an AllStar (AS) for the past two seasons, and demo'd a Rockstar L (RS) in Charlotte this weekend. For reference, I'm 5'9", 190. The AS is a better downriver boat, and feels more stable going over wave-trains and catching eddies. In my opinion, it lacks balance on a wave and requires too much edge to release into 180's or spins. That said, I've seen people above my skill level have no issues; so a lot of this is the indian, not the bow.
The RS to AS contrast is analogous to a Ferrari and a Camaro. Both are fast, but one is made for a very specific purpose that's obvious when you drive it. The RS in this regard is designed as a dedicated park-and-play boat, which is obvious when you start feeling the edges and realize all the volume went to the center, and not to the ends like the AS. I felt this additional center volume let my knees sit higher and more balanced, however this increase in stability was offset by the higher seating position, and thus, the more difficult roll and controllability.
The RS felt "right" surfing a wave, but it is unforgiving downriver and catching eddies/peel-outs, and requires a much more developed roll to execute properly.
Here are a couple of other reviews I found mirrored my experience. I hope these help: http://blistergearreview.com/gear-reviews/jackson-rockstar-m-vs-wave-sport-mobius-57 http://blistergearreview.com/gear-reviews/jackson-kayak-rock-star/2