Magic Image Magazine has a post up on Keanu. They said the following about his acting style below. Overall, it is a good read.
No matter where you stand, I don’t think you can watch Reeves’ Don John and claim he doesn’t understand the character his intelligence works its way through muscle and bone as well as heart and head. It’s performance as vibration. This might be the key to all that Reeves does an actor, including his magnificent gifts as an action star. Movement is acting, speaking is acting, listening is acting, just being is acting: Reeves reminds us of all that, often silently. There’s thought behind everything he does, and reading those waves of thought is part of the process of watching him.
Maybe Reeves is one of the few modern-day actors whose style fits that model. He doesn’t work elaborate origami folds to transform himself into a character; instead, he beams radio signals from within. With a trim crewcut or a lanky shag, with a stubbly mug or a clean-shaven one, with a scowl or a slow-burning smile, he’s always starting from the base camp of Keanu.