(sorry for the rant, but it's really all I can do at this point, and I really like[d? :( ] OW)
in the time since OW released, it has been on a long timescale average my most-played game.

There are some other good points in sibling comments, so I won't address those. The biggest problems I have are(in order):

1) It seems like they have moved from a Skill Based Match Making algorithm to an Engagement Optimized Matchmaker, or at least tipped the balance much farther away from skill based match-ups, and it really shows. Way too many games are a complete route one way or the other, and even in Competitive mode games are now often very uneven, where they used to be fairly balanced, and evidence suggests that they are using a stats based skill adjustment system rather than something like Elo that is based on wins. This would make using a non-skill based matchmaker for "Competitive" possible, and is evidenced by people getting placed in matches that have huge differentials in player rank even in metals ranks during primetime, something that virtually never happened in OW1 as far as I know.

This is really sad, and there is really a lack of awareness about these new systems and how, frankly, predatory the new generation matchmakers are. I've been playing competitive FPS(though often not competitively per se) for half my life and I'm rapidly being driven away from one of my favorite things. It's upsetting. Most people like winning, but when it constant feast or famine it really really really starts to feel like the games you win were just the MM giving you a win, and not earned.

2) They deleted a AAA, critically acclaimed, Game of the year winning game that everyone paid for, and replaced it with a buggy, janky F2P one. They removed a fair amount of content, and have had to disable 10% of the roster in the first 6 weeks because it's so buggy. They did add some content, 3 new heros and a handful of new maps, but it just barely balances out what they removed. And that speaks nothing to all of the other stuff that they removed from the UI, like Group finder. It also launched with some of the worst netcode I've seen in a non-indy game, players would briefly jump around the map before snapping back, extremely distracting in a game that is heavily based on tracking. OW1 never came close to this level of ineptness. Even today they announced a last minute delay to a balance patch that they have been promising for over a month, that was additionally supposed to re-enable a hero that has been part of the game since launch of OW1. Supposedly this is because the changes to a live service style, where they can easily adjust the game from the server side, which were-I guess-going to be a part of OW2, either weren't ready at launch or shipped in an unusable state.

But like, they could have launched OW2 as a F2P beta, and kept OW1 around until they had worked out the kinks, and then announced a sunset for OW1, or something they had already made it clear that OW1 was going to be replaced. Deleting a game that had an active playerbase of people who bought it and replacing it with a shittier, obviously half baked version, was a straight up dick move. Imagine if they did that to StarCraft when SC2 came out.

3) Meanwhile they removed one of the core features that got me to love Overwatch in the first place; it eschewed the "play to unlock" model that I have so learned to loathe as an adult, all heros and new ones were just part of the game. In OW2 new heros will be locked behind a battlepass. I have other problems with the F2P model, like it encouraging cheaters and low-investment players who don't know or care to learn to play a game that has significant depth around the cast of heroes(this is greatly magnified by the new Matchmaking which means that even someone who has >1000 hours will get in matches with them).

And to really rub the salt in the wound, they have been able to keep the new player shop filled with (shockingly expensive to this millennial) content. It absolutely feels like a cash grab at this point, especially considering today's patch delay(the second for this patch). It's also grimly foreshadowing that the hero that is currently disabled was only disabled because of an interaction with the hero that is currently locked behind the battlepass that let the new, locked hero get out of the play area and wreak havoc. Previously they would have handled it in reverse, especially considering the nature of the interaction (the new hero can teleport behind teammates).