I love how the story just starts. There is no voiceover. You learn everything you need to know about Wick from both his actions and how other people in the movie talk about him/react to him. The action sequences are equally lean; they feel real, violent, and believable. I was most impressed with how quickly Wick dispatches most of those who get in his way; he shoots nearly every person twice, once wherever and once in the head to make sure they are dead (like a real mob assassin would). Very few individual fights with people last for longer than 10 seconds and the longest fight sequences with multiple people usually don't last longer than a minute or two.
I was similarly impressed with the fact that nearly every stunt was a practical effect. This puts you so much more into the movie than seeing a ton of CGI people and effects (see my recent review of the Hobbit movies).
Another thing that surprised me was the fact the love story is entirely implied; Wick's wife is dead from the outset and you see his love and interest for her in the opening series of flashbacks and in his watching of the video of her on his phone (and, partly, in how the mob leaders talk about him leaving due to the love of a woman). It gives you enough backstory without needing any of it really in the story.
Keanu Reeves, not a favorite actor of mine, is surprisingly good and effective in this role. He is completely believable and at no time did I fall back on saying any of his Bill and Ted or Matrix catch phrases (which I usually do when watching him on screen). It's like this role was tailored to make the most out of him as an actor and action star.
Lastly, the run time is near perfection. At 95 minutes of movie (plus 6 minutes of credits), you don't feel antsy or like the movie is overly long. First act simply introduces the main characters and sets up the plot. The second act brings the main characters together and starts the action. The third act finishes the action and provides a brief denouement. Slam bam, thank you maam.
Is this film art or Oscar-worthy? Of course not. But it is a slick, lean, quality action film with a believable plot and really well-done action sequences. The main character is both likeable and well-defined. As an action movie I'd rate this an A-.