OK, let's recap:

At the end of FWWM, Laura Palmer seems to have found peace, basically ascended to heaven or whatever you might call it.

At the end of episode 9 of season 2, Leland has found forgiveness for his deeds, he has also visions of Laura as an angelic being (FWWM-ending) and joining her there. One must also keep in mind, that he also has been abused by Bob, it's heavily implied that he was molested by him as a child, not to mention the possession. So the redemption of both characters was well deserved.

Yet in Season 3 they are still in the black lodge. They are still tormented (Laura screaming, Leland having that stoned-out look). 

Cooper was reduced to a retard for the whole season, including episodes 17 and 18 - the Cooper in those episodes still was whacked out of his mind.

And the ending: An alternative reality has been created by Cooper yanking out Laura from the timeline. That means, nothing we have seen in S1, S2 and maybe even S3 happened! GREAT!!! It's like the Star Trek reboots.

We all know it's a TV show, but these "none of it really happened/dream/time line reset" etc. devices are utterly terrible, because they render everything you saw meaningless on some subconscious level.

Also, doesn't it render the whole "Laura being the chosen one"-angle that episode 8 was nodding at completely pointless as well? Laura's death set Bob's downfall in motion, but without her being murdered, Bobified Leland killed maybe a dozen more people.

Anyway, season 3 was just mean-spirited. All the Twin Peaks we knew has been basically erased, it never existed. Dale Cooper reduced to a caricature, which he never truly recovered from, many of the former characters got humiliated as well, like Lucy not knowing how a cell phone works in 2017 or their retard son, come on!

I don't want always a happy-end, but humiliating beloved characters and deleting the entire timeline is a bit much.

The ending wasn't even a "mindf*ck" as such, alternative dimension/it was a all a dream" plots are dime a dozen. The Lost ending was more of a mindf*ck actually, because I think no one expected that the LA scenes were purgatory/afterlife (didn't like that much, but it was actually more creative that this resolution).

No, that ending was more of a "F you". To the audience and Twin Peaks as a whole.