Most people argue that Season 4 is the worst season of Fargo, and Season 5 is a return to form.
I ... well, my first reaction to that is that if S4 is the worst, that's a pretty indicator of the quality. If you think of any series that has five+ seasons, I think you'll be hard-pressed to find any other one that doesn't have a season that is worse than S4 of Fargo. If you don't believe me, go through any standard list of "Top 20" shows and you'll see. Most shows either have a really bad season at the beginning, or more likely, a bunch at the end. Most of the exceptions are three- and four- season shows. I've done this exercise before.
As for me, I happen to agree that it's the least of the seasons, but I disagree that it is bad. I'd argue it's actually pretty good- but I think that the tonal shift and different focus alienated some viewers who wanted more of what 1-3 served.
If anything, I'd argue that the main reason it is just a shade below the other seasons wasn't the ambition, the acting, or even the shift- it was the pacing. But it didn't make it bad; just not quite as good as 1-3, 5.
Personally, my order would be ...
S2
S5
S1
S3
S4
But I'm open to arguments. Most people liked S5, but I really thought it was amazing. But that's, just, my opinion man.