1. You can find Genji's room in Nepal
It's easy to tell that Nepal is Zenyatta's hangout, what with the floating robot monk statues everywhere and all. But what the game doesn't tell you up front is that it's Genji's home, too. See, after being mortally wounded in a fight with his brother Hanzo and patched up with cybernetics, Genji came to Nepal to find peace with his old self and new prosthetic reality. That's where he came under the mentorship of Zenyatta, and the two have been close ever since. You can hear them refer to this relationship in pre-game chatter if you listen closely.
Since Nepal is Genji's adopted home, you'd figure he'd find a place to carve out for himself. And sure enough, you can find that on one of Nepal's three control mode maps.
On the Nepal map known as "Village" (which you might know as "The One Where the Control Point is a Tiny Room of Death), near the control point on the second floor you can find a peculiar room decorated with recognizable artifacts. On the right you can find a painting that should look familiar.
Sword-wielding brother? Check. Bow and arrow bro? Check. Giant dragon? You bet. It's not a coincidence -- this seems like a direct callout to the Shimada family.
It would seem as though Genji ninja-d his way back home to swipe a few choice artifacts.
On the left we can see a certain sword, and on the right -- aww. That's a snapshot Babyface Hanzo and Babyface Genji in better days. We don't get a lot in the way of characterization or development for the Overwatch cast outside of a comic here and and an animated short there, so it's nice to see something truly revealing hidden on one of the game's maps. Relics of Genji's past tell us that he still values that part of his life, including the brother that tried to murder him.
2. There's a giant dancing robot in Volskaya Industries
I don't know if you noticed but outside of the Volskaya Industries map there are a ton of giant robots. Seriously, it's like Pacific Rim 5 out there. They're all part of Russia's Syvatogor mech program, built to protect the country from the threat of asshole omnics like Bastion.
However you feel about their politics, you gotta admit these robots can jam.
It's tricky, but you can catch one mech pilot doing "The Robot" and pulling off some other moves in the furthest edge of the background. We don't know who's inside, but rest assured they're probably drift compatible with D.va.
3. Plenty of movie & TV references
Overwatch isn't shy about making pop culture references. In fact, they're downright shameless. Most of the obvious bits come from random one-liners from the crew -- Winston remarks "Don't get me angry," acknowledging the similarities of his Rage Mode ability with that of notorious green monster Mark Ruffalo. Other in-jokes are peppered throughout levels, often on signage. Route 66 is home to plenty of signs for "Deadlock Propane and Propane Accessories," a clear shout-out to gas grill salesman Hank Hill.
Some of the references are quite a bit older however, like this poster found in Hollywood:
"Some Like It Bot" is a dead-ringer for the Marilyn Monroe classic "Some Like It Hot," down to the instruments and high heels.
A little more modern-day but still obscure is a clever reference to Bill Murray favorite Groundhog Day, found in Route 66's diner.
When pulled over by cops after a joyride on his third consecutive day, Murray's Phil Connors jokes with the arresting officer by starting up a drive-thru order. "Too early for flapjacks?" has since become something of an annual meme, one that somebody at Blizzard is apparently a fan.
This last one is a little shaky, but someone brought up a convincing link between Overwatch and Big Hero 6.
On the left you can see Zenyatta's "Hello" emote, which is a circular "wax on" wave. As it so happens, that's exactly the same way that fellow robot Baymax waves hello. It might be a coincidence, but the two synthetic lifeforms are pretty similar in personality and vocal cadence that the connection is tough to deny. All we know is now I want Baymax in Overwatch and I'll never be happy again.
4. A touching tribute to a deceased fan
Many developers (including Blizzard) have taken to honoring fallen fans by representing them in-game, and that's just what happened with a recent patch in Overwatch. Blizzard must have heard about the tragic story of Wu Hongyu, a 20 year-old fan who was notorious among his friends for being a big fan of Captain America and of course video games. One day before Overwatch was set to release, Hongyu was killed while trying to stop a thief from stealing his friend's motorcycle. Following his death, local government bestowed Hongyu with a "Courageous Citizen Award," and Overwatch developers planted this lovely tribute in Lijiang Tower.
On the display of spacesuits, the center piece reads "Hongyu" in Chinese characters. The words above the suit roughly translate to "immortal hero" -- or as Mercy would say, "Heroes never die."