Jamstix is a really amazing piece of software. But you have to be prepared to sit down and really study it. Not just the manual, because the manual admittedly ain't the best. You have to experiment and piece together an understanding of the workflow and how Jamstix thinks. I'm not gonna lie, after using it a couple of years I'm still not 100% certain of what I'm doing. All I know is that the results are usually great, way above and beyond anything I could ever program myself in a piano roll, and way above and beyond anything you'd get from MIDI loops, even great ones.
Actually the best thing about Jamstix is being able to feed it one of those MIDI loops you have lying around, and having it use that loop as a blueprint on which it churns out endless variations and fills, based on all the parameters you have set up (drummer, style, the hundreds of "brain" options). It means, for example, that if you were making a straight ahead house track you could feed it a bar of MIDI with four to the floor kick, the snare on 2 and 4 and 16th note hats, and it would humanize that style and play around it.
To be honest I've never used the kits that come with it, because it's such a pleasure to hook it up to your favorite drum VST and have it go crazy. I've had it drive all of the Native Instruments drum libraries, Battery, Addictive Drums, various other Kontakt libraries and Geist. I've even had it drive chopped beats in Geist (with various results). Short of learning to become an expert finger drummer using your controller pads, I just don't see how else you'd come up with anything like Jamstix plays with regular MIDI. The guy obviously has a LOT of drumming knowledge and has managed to simulate real drummers better than anything else I've heard.
But that raises another point worth mentioning - I think the more you know about drumming, the easier you're going to find this program. Because the brain settings are very much expressed in real drumming concepts and lingo. I know sweet FA about drumming, so I find it a little tough going and very much trial and error. But I've had some stunning results from it. I just wish the interface was a little more intuitive and easy to use. Maybe Jamstix 4 will address these things.