Has anybody tried to evaluate the different rules engines in the interests of using it in their companies' technology stack?  I've got to do some due diligence, so need to evaluate the others.

Specifically, we're looking at a dynamic data model (not OO), and so that needs to be supported in some way (which I am heavily evaluating for drools :)).  There are plenty of other criteria, but the show stoppers are:
Also high on the list are:
So far I've found about 15-20 engines.  Hopefully most of them will fall out of the early criteria :)