>>7188009the characters have some interaction lines that can really open up the lore more. For example, everyone knows that Torbjorn HATES Omnics/robots. His interactions with Bastion when the game came out were always of derision. Over time though, those interaction lines have changed a little not as derisive as they use to be, but still a little blunt like an old man who knows he is wrong but won't admit it. and now that Torb's daughter is in the game she has lines that outright call out just how much Torbjorn actually cares about Bastion.
The environments of the maps can be dissected to help further the in game lore as well. Blizzard has hints to a VAST number of future heroes they have planned hidden in the levels, players are always piecing together clues in new ways or a new piece is added that makes the previous pieces no one noticed finally have significance. They often change some map details after a big event and/or cinematic short that correlates with 'plot advancement'
Finally they have been doing some PvE events that do give background story. Every year in springtime is a backstory event game mode that is PvE only.
but other then that, for a game that clearly has vast potential for lore building thanks to all these characters, it does have trouble really doing it super effectively if you aren't a super obsessed person hunting it all down.
which is a reason why I wish this went to MegaBloks instead of Lego. Lego works better for story telling imo, and Overwatch doesn't really do that.