I think the cops are just perfect in combat.
In IV, they were to easy. Luckely modding weapon damage etc... sorted that out.
NOOSE using teargas to get you out of hiding and cops dragging injured officers into cover is really nice as well. Really glad they brought all the good things about police from previous GTA games into this one. (rope rappeling like in the III era, spike strips just like in vice city (stories) and liberty city stories, randomised roadblocks (not only on bridges like in IV).
Cop combat is tough, but I don't mind too much. It's the wanted system that's annoying, along with their response time and psychic abilities the moment you commit a minor infraction in the middle of nowhere with no witnesses.
I have no idea what cars the cops are driving, but they move as fast as a photon that's late for an appointment. How is it that their vehicles are able to catch up to and ram from behind a fully tricked-out Adder, which is supposed to be the fastest car in the game, and be able to keep up with it?
Infinitely-spawning helicopters at 30,000 feet when you've stolen a jet from Zancudo? Don't insult my intelligence. At times, I wonder if I'm playing GTA or Saints Row.