John Wick is a film that knows what it is, who the potential fans are, where its actors' and characters' strengths lie, and which never oversteps any of those boundaries. As a self-contained film, it's nearly perfect; taken in the broader context of Hollywood it's a little derivative, a little pastiche and a little ridiculous.
Keanu Reeves is great in the titular role, in so far as anyone can be whilst embodying a character eerily similar to the lead in Taken with much less emotional attachment or charisma. Soulless is a little harsh to describe the performance, which feels very real (in a totally wooden sense), but if you remove the negative connotations it's also not far wrong. It's a little hard to explain but fair to say there isn't much in the way of range required to play John Wick.
Most of the surrounding cast are similarly two-dimensional entities, with clear roles, associated emotions and objectives. The idiot, entitled gangster heir is an entitled, childish idiot; the hard grafting, respected mob boss is a hard-ass, slightly terrifying monster; the morally oblique sexy assassin constantly double crosses people; the overly efficient receptionist is overly efficient, and so on. The same flat feeling can be found in the plot, where criminals have a strong moral code until it gets in the way of pacing or story development, at which point it goes out the window ("more a set of guidelines than a code, Ms Turner") and guns are magically never out of bullets until an opportune moment to reload presents itself.
Although, in fairness on that last point, at least the guns are routinely out of bullets. John Wick is not a film seeped in realism but you can tell the director has tried to make the action sequences believable. Guns do not have infinite bullets and the magazines they use are consistent in their capacity; reloading isn't easy and fight sequences frequently devolve into scrappy messes. It still takes an incredibly short amount of time to strangle someone and our lead can still take a level of punishment which would make Wolverine wince without either blinking or dying, but props where props are due: the action doesn't feel ridiculous. It's gritty, dark and frequently over-the-top, but it never crosses the boundaries it sets itself.
Plus, John Wick is choreographed sublimely. At the end of the day, the plot and characters are entirely derived to facilitate two hours of watching an extremely efficient hitman kill a huge number of people, so the fight choreography is where the film lives or dies. Luckily, it works brilliantly, with some completely ridiculous set pieces which leave you genuinely amazed. The stunt performers, including Reeves himself, are great and are backed up by perfectly smooth film work, with some wonderful 'one take' sequences, particularly the first real piece of action in Wick's home which has a fluidity to the camera which really stands out. Humour is placed well throughout the action to enlighten the mood at times and break up what would otherwise be a tiring experience, sometimes through dialogue but largely physical gags.
The result is a visually stunning collection of set pieces strung together by a good-enough plot and hung around the neck of characters with just enough, well, character for you to not care. Like I said at the start, John Wick knows what it is and chooses to just focus on that and do it well, which it achieves in spades.