House of Cards
While not the greatest show ever, I still liked it quite a bit, but that final season is the worst last season of a show I've EVER seen.
I understand that everything that happened with Kevin Spacey forced them to make huge changes to the show, but even ignoring his sudden absence the final season was absolutely awful.
Honestly it would have been better for all involved if they'd just not done the last season.
LOST
I really did not like the last season of LOST, more specifically as it aired week by week. Each episode felt like it took an eternity to come out each week, and then a large chunk of the episodes were taken up by the alternate reality "flashbacks" that were a big waste of time.
It was a torturous lead up to an ultimately unsatisfying conclusion.
It's like every mystery that could have been left a mystery was very deliberately answered (like Richard, Jacob, and the smoke monster's origin stories), and stuff that should have been explained more was just not (like more information about the Island itself, or why exactly the smoke monster leaving would be bad, or why the island had a giant, earthquake causing butt plug).
Even when I rewatched it years later (and didn't have to wait weeks for each episode) I still found it to be a really bad season.
Killing off Locke and having him be replaced by the smoke monster was a cool reveal in the previous season, but it meant one of the best characters in the show was just gone and replaced with a completely different personality. Locke and Jack's conflict was pretty central to the show for a LONG time and it basically never got a real satisfying conclusion.
And to go back to the alternate timeline/reality scenes, they were a BIG reason the season sucked. Because whenever someone died in the real world they'd get their memories back in the alternate world (purgatory orn pre-afterlife basically), it made every death in the final season pretty meaningless.
What does it matter if Jin and Sun have a horrible death or any other character? They'll be fine in the other world in the next scene.
It just sucks any drama out of a show when you know the characters are going to be fine in the next scene.
The very end worked on an emotional level since it was basically giving all the character's you've grown to love their happy ending in the afterlife, but from the perspective of caring about the overall story of the island and what was happening in the real world, it just boiled down to a stupid fistfight between Jack and not-Locke,and then Hurley and Michael go off to keep doing whatever the hell it was the Island was doing in the first place.