Kevin,
Any sort of evaluation definitely requires objectivity. Getting students to repeat recall-level questions is one thing. But, as you suggest, getting students to formulate rational conclusion (critical thinking) is somethong different. This takes an environment that encourages exploration, little penalty for guessing, application, and a of course, a solid theorectical foundation. Lot's of activities that can be introduced to the class to get to these desired results.
Barry Westling