#criticism is valid

The Main difference is Bashing doesnt offer ways of improvement and usually just portrays something as much worse than it is.

Criticism often points out what is wrong with said thing, and usually offers ways it could improve (if it is constructive).

First of all, no one is denying that the show is about brothers. But more importantly it was always about family. And, whether because of the pandemic or not, the family that the boys created outside of themselves over 15 years was excluded from the finale, except for Bobby. What about Jody? Claire? Eileen? Anyone from the alt world? It wasn't just left open-ended, it felt like they were forgotten. Plus, we had already got a brothers-only ending in 15x19, so expecting the writers to wrap up other storylines and such wasn't insane or whatever you want to call it. I could keep going on this point but this is the most general summary of this particular issue.

Second, Castiel was a very important character for A LOT of people watching this show. No matter their reasons, that's just fact. And those people have every right to be upset that he wasn't only physically absent from the episode, but was only mentioned half-heartedly twice. They are allowed to feel like the absence takes away from the overall ending. And that goes for any character people think should've been in the series' finale.

Third, who cares if a few people were "only mad that their ship wasn't in it" or whatever? It is no secret that many fans, and even casual viewers, of this show have felt queerbaited for years because of this ship. Then, two episodes before the finale, they get confirmation that one half of the pair feels the way these fans thought they did but no response from the other. Most people never expected Dean to reciprocate, but to never mention it again? Not only is it cruel to those fans, but it's just not good storytelling imo. So, yeah, I can see why people would be especially angry about that.

Lastly, though, most of the criticism of this episode actually lies in how Dean and Sam were treated. Go look at the reviews, read beyond the titles, and you'll see. Most of those reviews are about throwing away 15 years of character development. You'll even find many detailed, well thought out criticisms. Are some of the reviews more memes than critique? Yes, but everyone deals with disappointment and negative emotions differently. Even with all the bad energy, they still (mostly) manage to thank the actors and even apologize to them for having to be in the episode or for bashing them (Jensen) previously.

It's okay for you to have liked the finale. It's okay if you don't understand how others could hate it. But please, don't bash people for disliking it. Their feelings aren't invalid just because they're not yours.

And the same goes for the other side, as well. You may not have liked it (I sure didn't), but let's not hate on anyone who did. Everyone has different tastes and expectations, and it's nobody's fault how they feel.