My main amp is a RKI and I love it and they are like any other mesa, built like a tank. My friend has a roadster and i actually prefer my RKI to his roadster. I almost made the mistake of getting rid of my RKI and getting a roadster and I am glad I never did.
So considering the RKII is suppose to be voice just like the roadster, just with more options, I would probaly have to say I prefer the RKI over the RKII, but since i never played it I cant give you a complete yes on that.
No this is not the step child, probaly no one answered because there are millions of threads on the amp with many people that love it.
The RKI will get you what you want and it has great cleans as well, so do not let people say go with the RKII, it all depends on what you want.
Reasons why I like the RKI better. The brit channel is more voiced like an old plexi, gets you closer to the marshall tone then the RKII. Brit mode on RKII and roadster are more towards the stiletto, but with less gain, but still more gain then the RKI.
I can get just as much gain out of my RKI Brit channel with a booster pedal in front with the drive and the level maxed and it sounds just as natural as the RKII even though you are using some diode clipping to gain that gain! However what great albums from the past didnt use that as well?
Other things I love about the RKI, i have both a parallel and series loop, with the new RKII you get two series. I just like haveing the option of either one.
The Distortion channels have a bit more upper mid's then normal rectos and since i am more of a hard rock player with the occasional metal, I much prefer the voicing of the RKI.
As to the different in clean channels, going up againt my friends roadster, it is a bit noticable, but not enough for me to care!