The only downside about a Rock River is that you'll probably never get to know Tweak and the other fine folks in the troubleshooting forum...
...Oh wait, that's actually a [b]good[/b] thing [:D][:D]
In all seriousness you made an excellent, well informed decision. Currently the only ARs I own are Colts, but I've had a RRA, a Bushy, a DPMS, and an Olympic Arms. Although I openly advocate Colts my Rock River was every bit as reliable.
In my experience a Rock River is a Colt with standard hammer and trigger pins. Mine got sold because I got laid off and needed money at the time, not because I had trouble with it. My other non-Colts got sold because they fell far short of the Colt benchmark for reliability and trouble free ownership that I have come to expect.
Now that you have a new magwell to feed you will have to start thinking about ammunition and magazines to keep it well fed. You will probably want to accessorize it as well, but you might be better off getting to know your rifle in it's stock configuration first, before you start going crazy with new parts.
Good luck with your new black rifle. You have a lot of fun times ahead [:)]