𝗥𝗲𝗰𝗼𝗺𝗺𝗲𝗻𝗱𝗮𝘁𝗶𝗼𝗻:
First 3 seasons. At most watch till Ragnar dies because its all downhill from there.
𝗥𝗲𝗮𝘀𝗼𝗻:
This show went from producing highly anticipated episodes like GoT to be that show that you no longer like but keep watching, hoping it will get better some day.
Travis Fimmel's portrayal of Ragnar was one of the best moments in TV shows. For me the show most definitely died along with his character.
Also Gustaf Skarsgard's Floki was equally good.