I'd suggest that you be wary of going down the route of making your API too flexible. It becomes very difficult to scale up a service that provides flexibility.
Imagine a simple case where you're storing hundreds of records of users, and providing the flexibility to order by any field on the user, and of course, you're paginating those results. Now, scale up; you're storing tens of millions of those same record... how do you quickly retrieve the first ten records ordered by their e-mail address field? Same thing, ordered by their last name. Same thing, ordered by their country. Did you just create database indexes to support each of those use cases? Ugh.
In my opinion, a REST API (well, any API) should be limited to supporting only the business use-cases it is designed to implement. I wouldn't want to build a "Linq/SQL" type of interface, because then I have to support all the weird queries people will come up, and still meet my requirements to scale over time. Don't provide this kind of flexibility unless the value it gives your product is absolutely incredible, because, the headaches it provides could be equally incredible.
