McCree is a heavy hitting ranged Assassin who relies on his auto-attacks done by his colt revolver, Peacekeeper. Out of all ranged Assassin heroes McCree would cause the biggest ranged auto-attack damage. Imagine if Thrall was ranged instead of melee.
His auto-attacks combined with his Q (Burst Fire) and first heroic option (Deadeye) can be very deadly and finish off any unprepared squishy hero fast. However, the drawback is that he can't auto-attack constantly like all the other heroes can. McCree is all about managing the bullets of his Peacekeeper that works as his trait. A good McCree player would reload the gun regularly only a few bullets at a time instead of emptying all six bullets from the chamber getting a rather long reload time before he can start attacking again. You want to use all six bullets in team fights or while ganking to burst down enemy heroes and then run back to safety to reload. However, he got his own abilities to avoid damage and reload instantly as well as his own blinding grenades similar to Tychus' except that they blind enemies instead of damaging then.
Because of his reliance on auto-attack damage only McCree is very weak against blinds so heroes such as Li Li, Artanis and Johanna would be heavy counters against him. McCree however is very strong against squishy heroes such as Jaina, Kael'thas and Nova and other auto-attack relying heroes such as Thrall, Illidan and Raynor. His Deadeye heroic is very strong against tanky Warriors and Bounty Hunter makes not only McCree stronger but also helps his team to get more experience points getting ahead of the enemy team in levels.
This hero concept is pretty much finished but I would still love to hear your opinions, thoughts, criticism and ideas how to McCree as good and unique hero to Heroes of the Storm! Also if you got good links for ability icons I could use here please do let me know. I don't want to use the WoW in-game icons in this one.
Also, I'm just imagining him having a start conversation with tychus
McCree: Damn son, says here you've got a bounty on your head bigger than my gun
Tychus: I got a lot of things bigger'n your gun.
[Edit]: The heroics' level 20 talent options have been added.