Their loot crates are the same idea as their card packs in Hearthstone.
You get them for free after "X" event or reason.
You can pay for them if you wish.
HS they add to your collection to build/fight with and you pay for the cosmetics. HS is F2P.
OW they seem to just be cosmetic and dont help you fight. Although one could say certain skins can act as camo is certain situations.
While you pay for OW, they seem to give you new hero as they come for free. Unlike other games that are F2P, eventually you have to grind or pay to get a new hero.
HS allows you to "disenchant" cards to convert them into "dust". Then you can convert that dust back into any card for multiplied cost. Based on the type you want.
Packs and Crates seem to have equally lame percentages for "good" goodies.
I mainly mention the F2P vs paid aspect due to the video above and others that think/feel the same way.
Plus it is Blizzard. Pay them once for a constantly updated game. Not like they havent proven they wont just drop a game after investing into to easily.
And you give them $$$ to make more for OW, as well as make the next hit game.