I recently started watching this, and I’m assuming the general consensus is that the show really dips S4 onward? I think Ragnar’s demise was inevitable - both historically speaking and the way the show was going - but I don’t really like how it led up to it. Mostly with Yidu and him becoming a junkie. I hated the random 50 Shades of Grey and incest(?!) in France. Very strange stuff.
I’m not entirely sure why the show turned to 20 episode seasons either. That just leads to filler and hamfisted writing. The show lost a lot when it went from being very thematically tight with interestingly conflicting views (Ragnar/Floki v Athelstan/Ecbert) to being a grand ensemble cast of fighting and fecking. Concept of time has flown out the window too, it’s gone very Game of Thronesy with it.
That being said, at its best it was a pretty good show. A lot of iconic stuff from the earlier seasons — the Uppsala episode, the Blood Eagle ep, when they first land in England etc etc. I think I’ll carry on watching through at a more leisurely pace — I believe the next season is the final one, no?