Here is what Janet Burroway* says about action: "The significant characters of a fiction must be both capable of causing an action and capable of being changed by it." She defines action as "that meaningful arrangement of events in which a character is convincingly compelled to pursue a goal, to make decisions along the way, and to undergo a subtle or dramatic alteration in the process." Which is essentially what makes a great novel in my opinion; people changing and being changed by the events of the tale.
The Coldfire Trilogy by C. S. Friedman is an excellent scifi/fantasy example of this.
*I'll be referring to this book a lot: Burroway, Janet, Writing Fiction - A Guide to the Narrative Craft (fourth edition), Harper Collins, 1996, p.110.