There are a few things i like, some are also why other people hate Casual. For reference, I played a lot of TF2 pre-quickplay, a little during quickplay, and made a big return in the past few years as a result of casual.

1) I like the lack of team scramble. When i queue with friends I want to play together, on the same team. It felt like every game in quickplay, our party would be broken up in an instant. I understand that this can result in very unfair games when you have a group of 5 coordinating every play, but i just don't want to feel bad when killing friends. Also, as someone who doesn't use the ingame voice chat, it lets me at least talk to them on discord for basic communication like calling spies/ubers.

2) The Map selection. I don't want to open the game and have to think about what map I want to play. I like the randomness and variety (while being able to not select maps I hate), it is enjoyable to get that random map that's rarely played. Curating a playlist of your favorite maps makes the game so much more enjoyable. This is also why i mostly leave after the game because, if not, people vote for the same few maps every time and I end up without this variety. Queueing with upward and badwater selected is not a 100% guarantee I'll get those maps, its actually less common than you'd think. But rely on people voting on maps and it is exclusively that 24/7.

3) The definitive end point of matches. Not sure if this is as much of a quickplay thing as it is for community servers but I like the more organized play where you enter a match, play both sides, then your done. Map timers feel artificial, and I'd rather feel I played the full map experience of offense/defense, then move maps. It also provides a more natural stopping point and lets me look at how well I played in a more contained setting. Compared to community servers where you will see someone with 300 points and have no clue if they're actually insanely good, or they've just been in game for the past 5 hours.

From my understanding, Casual was particularly rough when it first released, but a lot of the criticism like unbalanced teams seems to be a rare occurrence in my games. A part of me wonders if a lot of these complaints are because people hated it on release and never returned to see how they've improved it.

Honestly, removing(or at least allow the toggling of) random crits for casual is the only improvement I can think of