In my opinion, the manga is very overrated. With a pretense for realism, there is nothing realistic in it at all. The manga is full of convenient developments, plot armor, unbelievable personality changes. Many characters look interesting at first, but eventually degrade into typical stereotypes from a shonen manga, losing any believability. Strategy and politics look realistic only until the main characters are getting involved, then things just start to bend conveniently to make the heroes shine.

The manga is not bad, by any means, compared to other similar works out there, but one shouldn't expect anything more than a viking-themed time-killer, and imho it certainly does not deserve its place in the top 50.