"The Vision" is an entertaining episode that keeps things going and has great atmosphere and character development (even if nothing very much in terms of originality) that fits perfectly within the "Vikings" overall story.
Ragnar is trying to convince people to join his team (and it doesn't seem he is having much luck). Bjorn, the 'new leader', is ready to leave for the Mediterranean. And Ivar is trying to convince himself that he can be a hero.
The episode does develop the teasing points that were introduced in the previous episode. Ragnar has lost the Vikings' respect, and in some respects his self-respect, but he is so keen to go back to Wessex that he doesn't care for anything. The plot makes him an angry and blind god that fits with the character's arc perfectly. Ivar's frustration is also nicely developed (sometimes without much subtlety, though). And Bjorn's mission helps to bring the point home of how much things keep going even when 'heroes' have fallen.
Even if the plot develops in a nice manner, the best in the episode is the gruesome and dreamlike atmosphere, and the character's relationships (always helped by the acting). "Vikings" keeps being a very interesting and enjoyable show (even if a little bit repetitive).