Well, I guess one more rant about it wouldn't hurt lol.
Aside from it being a rushed mess (as had been stated many times by many people) I have many issues with it. I'd say most if not all of season 5 (barring the finale) seems to be pushing for Jack to let go of the past and to stay to and save the future. The first, what, 6 episodes (I think) are all about Jack coming to terms with having failed to return to the past, how much pain his blind obsession with returning had caused him, and finding new meaning in his new present. He even finds some solace in the future, through his love with Ashi.
Speaking of Ashi, love or hate her, season 5 is as much her story as Jack's. Season 5 treats her as a central character that we're supposed to be invested in and root for. Just as the audience is supposed to be happy for Jack in his finding new purpose and happiness so to are we supposed to be happy for Ashi for finding those same things.
Other than that, season 5 goes out of its way to show the good that Jack has done in the future and the hope he's given to its inhabitants. In episode 6 (I think? The one where he was gonna sudoku himself.) we see communities with flourshing plant life and hopeful populations. It also goes out of its way to let the audience know there are now time portals left.
Everything about the narrative seems to set up for an ending in the future... and never delivers. Instead, the finale uses its last 5 min to suddenly change direction out of no where, shit all over the whole build up of season 5, and unceremoniously wipe everything the audience has formed any attachement to (barring Jack) from existence.
And before it's said, this isn't about "the ethics of wiping out a timeline." It's about the ending being unsatisfying. It's about being narratively blue balled DAMNIT!
Alright, there's my hopefully coherent rant about the ending.