The story is about a retired assassin whose name is widely feared and respected. Nobody gets in his way, but he retired when he met his wife. After some tragic backstory, some people get in his way, so he comes out of retirement to, shall we say, get some peace of mind.
First, this movie doesn't have much of a learning curve, there are a few opening scenes where the audience won't really know much of what's going on, but once you start to get a handle on the story it flows very linearly. There aren't really any subplots, and the characters' relationships to one another are very simple. There is actually very little going on with this movie, but that doesn't mean its bad by any means.
I think the best part about this movie is the fact that basically everybody knows the name of 'John Wick', and everyone is terrified of him. You are told that John Wick is a retired assassin, but mostly you are shown how good he really was in the interactions he has with other characters. You get the sense that in his prime he was some sort of Super 007. It works very well because very few stories in mainstream media are about an invincible main character whom nobody can really hold a candle to.
The sad thing is that I think this is also the movie's downfall. I understand that the story is John Wick is retired and hasn't been 'in the business' for several years, but since this is an action movie, you're obviously going to see him in action. The problem that you run into is that in order to make the movie interesting you have to have the hero at risk, so he will sometimes have trouble fighting against hired thugs. I take issue with that because in my eyes this character would be able to walk through anyone that tried to go toe-to-toe with him, even if he was out of practice.
I would say that the character having to 'struggle' for his victory is the worst part about the movie, because that's not who we are told and shown he is. We are given a man whom all the scariest and most powerful people in the world admire and fear, and then told that some random hired guns have a chance at stopping him. I simply don't believe that.
In my opinion, this movie could have been a lot better if John Wick's struggles weren't with the action sequences. We know he's going to win, we're watching this to see him kill some guys. But there could easily have been an obstacle in this movie that was not in his area of expertise, and watch him struggle with that. I know any examples I give offhand will be easy to shoot down, so I won't try to give any. But a story can be far more interesting if you give the character a set of skills and hand them a problem outside their area of expertise.
Overall, it's a good movie, and my suspension of disbelief isn't in his ability to manage to 'beat the bad guy', but rather quite the opposite. I would recommend it because of how simple it is, but if you're looking for some compelling story with several subplots, you probably shouldn't be looking for an action movie.