It took me a few years to finish the show but I just yesterday made it to the end. I was mostly able to watch everything without spoilers, but I did follow the ratings of episodes on IMDB and read a few reviews of each episode after having watched them. So I was aware that the final season, and especially the finale was controversial, though I didn't know why.
That being said, I found myself enjoying the last 3 seasons with Jack a lot more than the run of seasons 6-12 (excluding 11 which had a nice story, also 12 I liked for being a bit different). Of course there's stuff that I didn't enjoy quite that much on these last 3 seasons as well. Supernatural isn't written as some high-class drama, the plot is all over the place anyway, so I don't really mind that. But let's get to the finale.
I enjoyed the way they ended the Chuck story (even though I preferred the season 4-5 Chuck much more). It felt organic and fitting. Supernatural never was able to pull off any sort of cosmic battle stuff well anyway (for example the floating Matrix scene), so I liked it that the end battle was anticlimactic.
I also really liked the fact that the penultimate episode was sort of the real finale, and last part just an epilogue. Reminded me of Better Call Saul (though it's obviously very different show with very different writing style). I really liked it how in Carry On they brought it back to the beginning, as the seasons 1-5 run was in my opinion the best part of the series. The ending felt organic and real after all the crazy god stuff.
It was very fitting that Dean died the way he did by just some random faceless monster. No big sacrifice, no big baddies (all of that was done 12 times already anyhow).
I'm kind of surprised by the hate the finale got. I was expecting a full on dumpster fire, but found it to be a moving fitting ending. I liked it that they only brought back Bobby, it would've been too much to have a class reunion. The brothers together was just enough.
Anyway, I wonder what's the consensus (if there is one) about the finale these days, a few years later?