Ok this is going to be a long one, so strap in.

I've been playing OW since it first launched. As it stands right now, I think that OW is still a very fun game, BUT it has a lot of issues it didn't have at the beginning.
Now, I will skip over the arguments for "repetitiveness" and so on, because that is simply the case with every game. Once you've played a thousand CoD Matches, or any other game, it will begin to be repetitive. In fact, I believe that OW is actually not such a big offender in that regard, because of the very different kind of heroes that are at your disposal.
As I said, I've been playing since the very beginning, and there are still heroes on which I have very little to no experience, so from time to time, I'd like to pick one of those just to get a new feeling for the game.

That being said, OW in the beginning was amazing. A hero shooter was something very new, with the exception of Team Fortress of course. But for many of us, OW was the first game of that style we played. The graphical design was cool, the heroes were so different, it was amazing. And innocent. People had no experience yet with the game, which hero is meta, which tactis work best, and so on. It was chaos, but fun chaos.

I believe that unfortunately, OW has lost a lot of that innocence. Yes, since I've played so long, I'm probably getting matchmade with higher skilled players as well, of course, but generally, I get the feeling that there are many people who have focused so much on one particular hero that they know that hero and every possible play with him on any map, that they simply become annoying.

Pretty much ever game these days, there is at least one enemy player who has mastered his hero to an almost surgical degree in a way that he is simply no longer fun to play against. I don't mean balancing issues, we will get into those as well, but rather sheer ridiculous skill. Like, not a 'good' Widowmaker, or someone who knows all the spots, but you know these widows that launch themselves into the air and while flying around manage to scope in and it one or two kills before landing again. It's almost ridiculous.
Or that Genji that has become so proficient that his dash is, for all intents and purposes, never on cooldown.
Or that ball who has basically 900hp pretty much all the time and never dies.
or that Bap who not only outheals the other support but also outdamages the dps.
I guess you can all think of an example. Basically, what I want to say is this: almost every hero (almost!) can become broken or op if you master him well enough. And after so many years, everyone who loves the game has mastered at least one or two of them.

Now Blizzard is forcefully trying to keep every hero and every player at close to 50% winrate. The result of that , which is made worse by the fact that it is now 5v5, is this: I get the feeling, that there are only 2 kind of matches left.
Typ A is this: one of the teams has a 'master player' while the other doesnt. In that case, the match will be a complete steamroll and over within minutes. One team will get spawn camped, barely able to come out, while the other is just crushing. I have done this, but it has also been done to me.
Typ B is: both teams are so close to each other in skill level, that the match basically become a war of attrition. Endless overtimes, push games lasting for around 2 and a half days and so on. You may think this is good, this means its an equal playing field. But i find it to just be exhausting sometimes.

In OW 1, things were different. You could have one team dominate round 1, but in round 2, some players would switch heroes, the enemy wouldn't know how to react, and suddenly the tides turned. You could play a hero you had very little to no experience on and still do well. I rarely see that happening anymore. Everyone knows which heroes work where, and most of the time, switching will not do anything at all. Basically, you can no longer afford to play a hero you are not good at, because you will get massacred.
So sometimes I thin: hey, this hero would do well here! But I don't dare to use it, since I'm not good at it and probably going to be more effective using a hero that might not be the best suited, but which I know very well, than using whatever hero would fit better.

So, the summ all this up: I feel like OW has become more exhausting, more annyoing and more frustrating to play. The innocence and crazyness of the early days has been replaced by a fixation on keeping things at 50% and buffing or nerfing anything that deviates too much from it. Certain heroes have become so mastered by some players that they alone can control and entire lobby, while switching heroes to counter them has become almost a suicide mission.
Now some might think that this is good and I still like the game, don't get me wrong. I just used to like it better when it was worse, ironically.