(I wasn't spoiled to anything specific in the last season...except for one relatively big moment...but I'd heard fans hated season 4) and my need to complete what I started. I'd already rewatched the first three seasons--seasons 1 & 2 are brilliant, IMO, and season 3 wasn't as bad as some fans thought when it first came out--and want to rewatch the fourth season ONCE, and not again.
One of the worst parts of season four* is Megan Mullally and Nick Offerman have key roles in the show and I desperately wanted to like their characters, as I like both of them. But I didn't.
* the biggest mistake the writers made in the last season of the show was basically trampling all over the message the first three seasons send that family is everything. Things happen in season 4 that are so egregiously out of character...and it never really gets righted in the end.