A Gothic Cathedral Is Just a Bunch of Rocks Put Together: The Genius of Overwatch

I have been playing a positively disgusting amount of Overwatch, to the point where I'm starting my day with the stated goal of "Don't just play Overwatch all day", and I'm occasionally failing. This game just hits all of the pleasure centers of my brain just right and I just want to play it for hours.
The thing that makes Overwatch compelling, in my opinion, is how many interesting interactions arise from relatively simple mechanics and abilities in the game. Generally speaking, every character has a gun with a regular and an alt-fire, two abilities, and an ultimate that can be triggered when a meter is filled. That's really it, and while it might sound imposing all listed out like that, compare that to the variety of weapons and playstyles for any one character in Team Fortress 2, or the sheer number of loadout possibilities in a Call of Duty or Battlefield style shooter, and 5 main ways to interact with the game seems....sparse.
The thing Overwatch understands is that you can create extremely complex and compelling gameplay out of some very simple mechanics in interesting combinations, the same way the most ornate Gothic cathedrals are just simple rock rectangles, arranged in an interesting way. These combinations largely work in the way you'd expect, despite not necessarily being obvious. For instance, Genji, the cyborg ninja, has an ability that allows him to reflect any projectile sent his way for a limited time. His brother, Hanzo, has a devastating ult that sends forth an arrow that transforms into massive energy dragons, travelling through walls and dealing tons of damage.
Genji cannot reflect the dragons, which is what you'd expect: they're large, not really tangible, and seem less like projectiles than sentient spirits. However, astute players will recognize Hanzo's ultimate starts out as a simple arrow before summoning the dragons, and astute Genji players will recognize that this arrow can be reflected. If you're Genji, and you're attentive and skilled enough, you can be rewarded with a great play in reflecting this ult.
The "Dragons" animated short Blizzard put out, which features Genji and Hanzo, actually hints at this interaction
The game is full of these interesting interactions, which make for exciting techniques that master-level players can perfect, and can properly separate advanced players from beginners. Reinhardt can charge D.Va's self-destructing mech away from his team, saving them. Mei's wall can also be used to give someone instant high ground, great for McCrees hoping to land a clutch Deadeye. These interactions are layered on top of each other in a six-versus-six game, to create a series of situations with deep, deep complexity.
Another key component to Overwatch is, I believe, Blizzard's mastery of game feel. For being a title in a genre completely foreign to Blizzard up to this point, the gunplay feels great. Every gun, from Tracer's pistols to Roadhog's shotgun, feels good to use, and the hit markers and headshot indicators offer excellent feedback. But, more than that, every character, no matter who they are or what they do, when played at their best, feels good, and moreover, feels good in a unique way.
When I'm having a good day with Roadhog, I almost feel like a hunter, or a predator, grabbing people out of the air and reeling them in, watching them helplessly look at me while I line up my shot. When Reaper drops down from an unseen alcove and begins his Death Blossom, you feel like a force of nature, like Death itself. When you play Junkrat right, well, in his own words, "everything comes up explodey".
Compare this to other multiplayer games I really like. In Left 4 Dead, all of the humans have the same playstyle, and you cycle through the Infected so fast you can basically consider them all one, homogenous playstyle. In Assassin's Creed, the one way to play is "quiet, slow, and stabby". Even in fighting games, characters don't tend to stray too far from the sort of ur-style of that game: anime fighting game characters are fast and airborne, NetherRealm game characters are slow and plodding, Marvel vs Capcom characters are twitchy with a bunch of ranged attacks, etc.
This, I feel, is the key to Overwatch's longetivity. Talking with my friend the other day, I realized that I haven't played any game other than Overwatch since it's release, literally. If I had to guess, I'd say it's because whenever I get tired of the playstyle of Overwatch, instead of switching games, I simply start playing a character I haven't played in a while. When I'm sick of picking off targets as Roadhog and Widowmaker, both of whom are characters heavily reliant on careful selection of targets, I pick up Reinhardt and Reaper, and get in the middle of the action. When I'm done with them, I play Junkrat and Symmetra, and adopt a playstyle that's much more anticipatory, and based on traps.
Junkrat is also very good if you wanna make a bunch of shit explode
I love Overwatch. I think the characters are all unique and interesting, both from a visual and narrative design perspective, and in the different ways they are all satisfying to play. No two characters fulfill the exact same roles, and when you combine this with the interesting way all of the characters interact with one another, and the little tricks each character has that only high-level players can learn and know, and you get a game with a ton of depth, and a nearly infinite ability to engage.