I’ve watched the Vikings fly on the wall documentary on Prime and to be honest, the idea of a river cruise along the same sort of lines quite interests me. Not keen on the human sacrifice side of things, but they seem good on partying, robust interactions with local people and Scandinavian martial arts. I guess they may be unpopular with local people during shore visits, particularly monks and some women, but I guess that’s just tourism for you.
Stuff I’d bear in mind would included making sure that you’re competent with axe and/or sword and shield before going – maybe get some lessons in advance – never argue with the ship’s captain and steer clear of anyone wearing really badly-applied eye-liner. Oh, and try not to sack really large cities, Paris for example, as it rarely ends well. Apart from that, it looks like a good, fun sort of gig.
Edit: to be clear, I’ve never been on a Viking river cruise myself, just watched the documentary. They seem aimed at a younger, more adventurous demographic.