The 'main' action scene where Reeves storms that club and takes down a series of bad guys is not at all realistic.
The techniques he's using are. I also liked how he is fairly no-nonsense with killing them... but then the script has him take moments out to do unrealistic things, for the sake of making the scene more interesting.
When a target is hit but not eliminated or even porperly downed, you really shouldn't waste time fiddling about grabbing spare magazines and reloading, when there's a ton of alternative weaponry to hand that would simply kill them outright and then let you sort your firearm(s) out without being under immediate threat.
He was also pretty wasteful with the double and triple-taps, when he's shooting from 6" away... If you can kiss your target, you can certainly put one directly through their skull and save ammo.
What gets me is the "revenge" on one man, I must murder 50 people who are just doing a job,
In order to get revenge, he must kill Theon Greyjoy.
In order to get to Theon, he must kill a bunch of people.
In doing this, he will anger Theon's dad, which will mean that bunch of people and a bunch more will either try to stop him and/or come after him once Theon is dead. The more he kills now, the less he has to deal with later.
If that happened to my dog and I possessed the skills of Mr Wick, I'd do the same as him.
Even if not, I might still give it a go...