LINQ2 supported creating queries from expression trees via the MongoQueryProviderImpl.CreateQuery (non-generic) method.

This mechanism is used by the Dynamic LINQ (it first converts a textual query into an expression tree and the passes it to CreateQuery).

LINQ3 doesn't provide an implementation of this method (MongoQueryProvider.CreateQuery just throws).

It should be simple to re-add the support for LINQ3 as LINQ2 simply used reflection to create the fully typed query object.

I'm unsure if this was deliberately omitted from v3, apologies if that's the case.

Many thanks