McCree isn't a complex character, he's a hard living, plain talking cowboy that shoots whatever he's in front of. He loves announcing that it's high noon even when it isn't (although, as he points out, "It's high noon somewhere in the world", so fair play to him). He might seem like an easy win to play as, but he's got his own challenges to overcome and quirks to learn. This guide will give you a few good bits of advice to make the most of the urban cowboy, as well as which heroes he should avoid.
In a straight fight McCree is a safe bet. His pistols are deadly at short to medium range and combined with his abilities he can beat almost any hero in a mano e mano fight, but he can't jump around the map and take side routes. What this means is that you can't run him smack dab into the centre of a pair of tanks and expect him to win. At the same time you don't want to stray very far from the main group, because McCree can't evade that well and needs some backup and support. Your best bet is to stick around the edge of the main brawl and pick off the more isolated players one at a time.
Because McCree isn't a flanking hero it makes him vulnerable to being flanked, especially since he has lower speed than his fellow offense heroes. On the flip side, however, McCree is very good at countering flanking heroes because they're usually strung out on their own and he is, as we just mentioned, very good in those situations. As a McCree you can effectively look out for your entire team's back as well as your own.
McCree deals good consistent damage up close but if you're caught in a firefight, or moving up to the fight and taking damage, he'll do well with some extra protection (especially because McCree can be vulnerable to long distance sniping). Stay behind Reinhardt's shield and shoot from there, take cover under Winston's barrier dome, or get a projected barrier from Zarya to raise some hell. Work with your tanks, because it's in their interests to make you combat effective as well.
Imber is a contraction of 'imbalanced', used here because people complain about McCree combining his Flash Bang with other attacks being too powerful, the bitterness of their tirade indicating how recently they were killed by a McCree doing this. The Flash Bang ability is what makes McCree so deadly in a fight. If you've got good enough aim with McCree you can use the Flash Bang to stop an enemy dead and then use the secondary fire on the Peacekeeper to unload an entire clip into them while they're still stunned. The amount of damage this does is enough to take out basically any hero out there – apart from the tanks. So don't hang around up close to the tanks when the Flash Bang wears off.
McCree's Combat Roll ability can help get you to cover, it's true, but its secondary, and arguably more useful, application is for getting a quick reload in the middle of a fight. The roll makes you a harder target for your enemy and you can come up firing. It's particularly satisfying to use against someone who you've nearly killed, and is now trying to disengage and run away.
Deadeye, McCree's ultimate ability, is a thing of beauty. It can take out an entire team in one go, depending on how lucky you are. Getting a good Deadeye is a bit of luck and a bit of judgement, but there are things you can do to give yourself a leg up. Deadeye works on McCree's line of sight, so if you can get some height and improve the field of view you've got on the enemy team that's an advantage already. Coordinate your attack with your teammates if you can: if you use Deadeye at the same time as Zarya's ultimate, or with Mei, then you're aiming at enemies who can't get away as easily; Reinhardt's shield can give cover while you're aiming; Mercy's damage buff makes the attack even more deadly.
Widowmaker presents the most continuous threat to McCree. His weapons are next to useless at range and Widowmaker can eliminate McCree without having to get anywhere near him. Soldier 76 is dangerous for the same reason: his weapon has a much longer range than McCree's, and his ultimate makes targeting a non–issue. This kind of thing is why we told you to work with barrier tanks above.
McCree is great against the fast flankers like Tracer and Genji, stopping them in their tracks with the Flash Bang. You can also use the Flash Bang on Mei, as well as Torbjorn and his turrets, and it can get Pharah out of the sky if your aim is good enough. Pharah is also really vulnerable to McCree's ultimate, because she's often in the sky and will therefore often be in his line of sight. McCree can also take apart fleshy tanks like Winston and Roadhog as long as you approach with caution. They present pretty big targets to shoot at.