Season one was great, honestly it was better than most, but season two is when you truly see the amazing plot and are really hooked to this anime. Many people might complain that season two is trash, but that's because some people are unable to comprehend good character development.
I will say I was a bit skeptical at first when I began season two, but when I saw Thorfinn's change and how he truly did strive to be better I finally understood how amazing this story was. At first I thought Vinland Saga would be like those only action focused anime that had almost no plot and nothing to learn from it, no offense to these types of anime since I do also watch and enjoy them from time to time, but I found myself pleasantly surprised when it wasn't. In fact this anime was so good I went and read the manga, I would definitely recommend this anime if you aren't looking for mindless violence for the whole anime and for well written characters. From my experience, this anime is one of if not the best anime I've ever seen.