I didn't actually know anything about the film before I went, aside from it was showing at the more art-y theatre and it starred Robert Downey Jr and Val Kilmer. That seemed like enough of a recommendation to me.
It turned out to be essentially a buddy detective story, patterned after detective pulp in a smart, self-referential way. It's very funny and the dialogue is sharp and witty.
Highly recommended. I may even see it again.