Overwatch intentionally plays enemy sounds louder than allied sounds. That explains a lot, actually.
Source, the game itself:
Overwatch launched with the hype of a thousand summer blockbusters this week. From the exceedingly private closed beta to the insanely accessible open beta, potential players, fans and everybody in-between were frantically anticipating this title from almost its inception.
I thought nothing of it until I got my hands on it thanks to the timely intervention of a friend who happened to have a key during beta. It was then that I became a believer, though not for the same reasons that everybody else might have.
I primarily played League of Legends prior to playing Overwatch. League of Legends is a very different game in many regards, but objective based gameplay is a key similarity. The objectives may be different, but teamplay will beat out any one sick mechanical player in either game (unless you're Faker).
Upon playing Overwatch extensively, I started to notice that most of the cues in the game are based in sound. You hear the sounds of gunfire from long distance, at times long before you see it. You hear the sound of footsteps that sends shivers down your spine as you ponder if its friend or foe. Crucially, you hear heroes call out their ultimates as they throw them down, often being audible from the other side of the map. "Hammer down!", "It's high noon!", "Justice rains from above!", to rattle off a few that anybody who has played even a few maps of Overwatch will understand.
It gets even more interesting than that. Depending on which side the hero is played on, the vast majority of heroes have a different ultimate line. I first noticed this through Mercy, who has a line in English ("Heroes never die!") for when an allied Mercy uses her ultimate, and a line in German ("Helden streben nicht!", lit. "Heroes Do Not Die") for when an enemy Mercy uses her ultimate.
On the whole, if your hero is bilingual (Genji, Hanzo, Zarya, Mercy, Mei), they will use an English line if they are allied and use an ultimate, and a non English line if it is an enemy ultimate. In addition to that, several heroes further have a line for allied and a line for enemy ultimates. Examples include Zenyatta ("Experience Tranquility" vs "Pass into The Iris!"), Soldier: 76 ("Tactical visor activated." vs "I've got you in my sights!"), and many others. They also have a nonunique line when you are playing as the hero and you use their ultimate.
While "Tactical visor activated." is an allied Soldier: 76's ultimate battle cry, "I've got you in my sights!" is what you will hear if you are playing Soldier: 76 and use his ultimate, even though that is otherwise the enemy Soldier's ultimate battlecry. Though enemy Zarya uses her Russian line "Ogon po gotovnosti!" (lit. "Fire ready!"), so too do you if you are playing Zarya. Her allied ultimate battlecry is "Fire at will!"
Going back to League of Legends, the game is chock full of visual cues. There are plenty of little icons that pop on your champion's head, shoulders, hips or along the ground you walk on depending on what champions are in the game, what map you are on, and what items you have.
All of these different little animations mean different things. You have to know what all of them mean, and then you also have to know what is going on not only around you but on the minimap to do well in the game. All of the information you gain is visual in nature. While there are audio cues in the game for global abilities (Rek'Sai ult, Sion ult, Karthus, Soraka, etc.), they are few and far between compared to Overwatch.
On the same token, it isn't to say that Overwatch straight up doesn't have visual cues. They take the form of projectiles, or heroes acting erratically when they pop their ultimate. But again, they are (in my mind at least) not as "loud" as the audio cues ingame are.
Ultimately it is a battle of preference. Do you prefer to be able to take a singular glance at your minimap, warding positions, allied champions and enemy champion guesstimates and act from that? Or do you prefer to listen for audio cues and assess the situation in that way?
Sound off in the comments if you like!