I bought one when I started bushcrafting but sold it shortly afterwards and bought a sabre 45, I found the rocketpack sat too far up my back, I believe they are made so that you can wear webbing underneath them.
I find that with mine too. The rocket pack is designed to fit above military webbing (belt kit) and as such doesn't sit on the hips properly when used without webbing. This puts an awful lot of strain on the shoulders. I'm 6'1'' by the way, and as such have quite a long back.
I also have a slim physique and find the straps don't really adjust to the size I would require to restrict movement of the pack when hiking.
And if you have a full load in the pack the rain cover won't cover the side pouches. That's with the pack at capacity, not overloaded.
Also, there are no straps on the bottom of the pack where you can sling a rollmat etc. This isn't really much of a problem as I tend to strap it on the front with the bungee attachment.
The pack itself is very strong though and I can't see mine breaking any time soon. I imagine it would do the job it's designed for very well (military use) but I don't think the design translates well into the civilian market
If I had the choice again, I wouldn't buy one. I'd chip in an extra bit of cash and go for something like the Sabre 45.
I hope you have more success with yours. I know there are quite a few happy Rocket Pack owners out there.