Plenty of voice. Apparent stakes. Some conflict (or the promise of action) -- but keeping it in balance with other elements and not starting it too soon. A logical unfolding of events. Succinct sentences. A sense of intrigue.
These are just some of the elements that (might) go into the tasty soup of an excellent story opening. While acknowledging that not every great opening will have every element, agent Susan Hawk illuminated this tricky and crucial aspect of writing with loads of examples.