New Kemper user here and high gain lover, so I feel it's wise for me to give my feedback at least for the things I have tried.
I started trying some free rigs to start with. It was OK. Definitely better than Amplitube 4 that I was using before but it didn't give me that Wow Factor I was expecting and had heard about.
Then I went and bought SimMix's Producer Pack I. I planned to do a quick trial of all the amps in the pack or at least that was the initial plan.
How little did I know.
I played for 4 hours straight and I've managed to check only 4 of the 19 amps included in the pack. (Randall Satan, Engl Savage, VHT Pittbull and Hesu Little Bastard)
I liked them all but I fell in love with Engl Savage profiles. If you told me that this will be the only profiles you'll use from now and on I'd be OK with that.
Definitely a thumbs up for SinMix on that one!