For me it's the combat. Or rather, the puzzle-problem-solving aspect of combat. I like tactical planning and seeing a plan execute perfectly (and I've got some Red Alert stories, among others...) I like logistical planning (games like Railroad Tycoon 2 and similar). And I like strategic planning (games like Risk.)

__________________
[Dr. Horrible]___________________________[Penny]
Listen close to everybody's heart________And you believe there's good in everybody's heart
And hear that breaking sound_____________Keep it safe and sound
Hopes and dreams are shattering apart____With hope you can do your part
And crashing to the ground_______________To turn a life around