OPA, or rego? My experience working for Styra was that most people seemed to grok where OPA fit in fairly quickly, but struggled with rego. It's a very powerful language and well worth learning I think, but it's an investment for sure.

I agree, Rego was a hell of a thing to try and figure out.

Rego is a DSL and the main purpose of DSLs is to simplify things (compared to general purpose programming languages), so in my opinion Rego is not a good DSL.

Used it during my last gig for policy enforcement on a multi-tenant platform for internal applications.

I found it relatively easy to use and at a good level of abstraction to make the policies relatively reusable.