I recently moved from a SuperStar to a RockStar L, I've been meaning to write something up on the transition and this seems like a good time.
I am about 185-195, currently 185, 5'9", 32 years old and playboat alot and creek boat a little. My weight puts me in the "optimum freestyle" category for the the boat. I cracked my SuperStar, and I had already cracked and replaced it once before so the warranty was out once the new hull came in. So I sold that and moved into the RockStar without demoing.
If you've read other reviews then you've heard it will feel super unstable the first few times you paddle it. This is true. My first run on it was Upper Blue at 1700. Normally I could run this section in my SuperStar without so much as a paddle but now in the Rock I was high bracing constantly and had 3 real combat rolls. It was extremely squirrelly feeling comparatively. After a few more runs here and there, I now almost can't tell the difference. I do think the change helped my overall down river paddling, my creek boating has improved and I feel more stable all the time now. I think that is a result of paddling a tippy little boat on easy rivers. One note, the move to the RockStar made the line between when I use my creekboat and when I use my playboat much more defined. In The SuperStar there was always a lot of of overlay, for instance I might run Pine Creek in either at lower water. But in the RockStar I have no plans to run Pine Creek in my playboat.
For actual playboating this boat is a noticeable improvement over the SuperStar. It surfs much faster, especially on little waves. I had read this and was skeptical, but its true. It spins easier too and is generally more fun to front surf if thats where your abilities are at. It cartwheels easier too. Bow and stern stalls are easier, and cartwheeling in a hole is easier and you can go much shallower, which is surprisingly noticeable. Loops are where the biggest improvement lies at my skill level. Plugging is so much easier I don't know just how to describe it. And it plugs deep and loops huge. I find myself looping tiny river features that I hadn't even considered before in the SuperStar.
On it being weaker plastic. Maybe. Take the screws that hold the seat to the frame out and sit in it. It wiggles like hell. And yes the whole boat is softer if you step in it etc. But I really don't think I can tell out on the river. I think more importantly, Jackson stands behind their warranty. I cracked my SuperStar in year 1 of the warranty and again in year 2. They replaced it twice, each time rapidly and easily and at a total cost to me of $100. In my opinion thats the best argument for using the hell out of your boat and if you are on the fence between a Jackson and another brand, then let the warranty decide for you and go Jackson.
My overall verdict is yes I am very happy with the Rockstar. However, I would go Star series if: you are only going to have one boat and want to start pushing your way up into class IV, or if your idea of playboating is front surfing with the occasional spin, maybe a squirt, and you aren't trying to rapidly improve. I would go RockStar if you want to use it to strictly playboat or keep the river class to III, or if you are also running a creekboat for harder stuff.
On top of all that, and other all things being equal I would go Rockstar.