It's cheesy, formulaic, and hammily acted. It's also stylish, high energy, and generally just a fun popcorn movie.
"John Wick" is a retired hitman who gets brought back into the life by a personal attack (no spoilers here, but if you're squeamish about animal cruelty, be warned). Okay, we've heard this story dozens of times.
What's different is the world in which this takes place. There's a secret criminal underground that seems to have their hands in everything, and there's a specific code and honor among thieves. Actually, come to think of it, we never really meet anyone who isn't involved or in the know somehow, so it's implied that this society is very widespread and possibly runs everything. This film actually seems to have more in common with the "Wanted" comic book than the "Wanted" movie did.
Part of the style and identification with the near superhuman Keanu Reeves as Wick is that he isn't a perfect action hero. He gets hurt. A lot. Unlike Neo, he's not invincible. He's simply very well trained and determined, which makes the combat sequences more interesting because, even though you know the outcome, there's always this little part in the back of your mind that wonders if he'll come out in one piece, making them gritty and...semi-realistic. Let's be honest, a lot of the action moves are very theatrical and wouldn't have much practical value in the real world.
Given the implications for how big this criminal underworld probably is, it seems to have been set up to be a franchise from the start. From background characters like Ian McShane's Winston (who keeps referring to Wick as "Jonathan" even though the name is John; different spelling means it isn't a shortened version of his name) to Lance Reddick's hotel manager (who I would swear there is more going on with this character and hopefully gets explored later), there's a lot of ground to explore. It's not a smart or challenging film, but it is fun and not a bad way to spend a couple hours if you like action movies.