I'll just reiterate what has been said already, from my own perspective:
1. Rag Dolls are supported. You can't make a professional looking animation system without rag doll deaths these days. If you're making an RTS, or maybe a strategy game, where character animation is not particularly important, you can get away with it. For a professional looking FPS or third person game, you need rag dolls.
2. You don't need to get your user to install a driver. It feels quite unprofessional to me to force a user to download and install a driver which leaves various EXES and stuff in your start menu. With Dark Dynamix you just bundle the DLLs and you're done.
3. Matty has put more effort into the vehicles and although I've only played with the demos he's produced, they feel more solid already. I think better vehicle simulations will be easier to achieve with Dynamix.
4. Matty is around supporting this product. I'm pretty sure he dreaded the problem of boned rag dolls, but after the forum (probably me mostly!
) made it clear we wanted them, he went off and tackled the problem and got them into the next update. So basically we have a capable developer who is listening and actively working on the product. That's like gold dust, because it's impossible for all the bugs to be ironed out in the first version.
Having said all that, if you just want to dabble with basic primitives and joints and mess around, Dark Physics will be more than enough.