As many reviews on season 4 pointed out that there are multitudes of SJWs connected writing here, I am going to ignore that aspect and give you my overall thought:
******TL;DR: Watch it, and you will be left disappointed and confused******** ********************************
If you have not yet watched the entire show, don't watch it because its ending will leave you with a bad taste. Please don't waste your time on this. But if you have started already, or felt the compelling need to watch it, I would only advise taking the show with a big sack of salt.
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Now, I won't be spoiling the season 4 much.
1. The '1-year' gap
-Except for the overall storyline, there is a lack of connections from season 3 that lead the season finale storyline. The story of season 4 would start "1 year" after the event occurred in season 3. Suddenly, you have unnecessary things added to the main story that doesn't fit with the overall flow of the story at all. Worst of all, the sin which the writers committed is not thoroughly explaining that '1-year' gap. Ultimately it let the audiences feel more left out on the transition from season 3 to season 4, making the starting point of the season finale confusing.
2.BCR, a modular role popped out of nowhere.
-One of the many examples is the BCR, the Black Communist Rebellion. The role which it played in season 4 has very little importance on the overall story aside from one part. Moreover, its placement doesn't fit in overall HIHC universe at all, not even in the ending. So in season 4, you suddenly have this military organization come out of nowhere in the writing, taking major screen time in season 4, which would've been better if it were the resistance instead.
Overall, BCR's role in season is very modular, adding an unnecessary plot and new set of characters to season 4 that seems to be the replacement of the plots and characters coming from season 3. It feels like the storyline and ending wouldn't change even if the writing team take BCR out of season 4.
3. Missing characters
- Where are Ed and Jack? Where are the other characters from previous seasons? Those characters are NOWHERE TO BE SEEN in season 4 finale. Perhaps Ed can disclose what happened in S3 to Juliana, which would add more drama to the show. Hell, maybe ACTUAL Tagomi appears in the show for 1 episode.
Do you want to see these characters in season 4? TOO BAD! Because you will never see them, NOT EVEN IN THE ENDING!
-Why? You ask? It's obvious that the studio cut these actors out of the show. For what reason, I do not know. But cutting important reoccurring characters out has hugely down-played the potential of the season finale.
4. Lackluster ending
- I am baffled to believe the writers would even consider it an "Ending". Why? Because I genuinely believe that a children's book written by a 10-year-old would have better clarity of a conclusion than that low-grade writing as the studio presented in the season finale. I don't know what the writers are trying to achieve here with the last episode. I am more confused than ever.
********************Final Words:
I suspect that the studio had its funding cut and thus you get this inferior writing and production of season 4's story and ending. It makes sense when the ending is not thoroughly explained. BUT I might be wrong.
It was a good run from season 1 -3, sadly season 4 is a finale that disappoints.
If you have not yet watch the entire show, don't watch it because its ending will leave you with a bad taste. Please don't waste your time on this. But if you have started already, or felt the compelling need to watch it, I would only advise taking the show with a big sack of salt.
RIP Man in the High Castle