I'm on the last of the 3 islands and a few minor missions away from the end of the game.
It has taken roughly 30 hours on easy to finish but that includes 2 hours or being totally lost

To sum it up it is a damned good fun hack and slash game very much int he vein of Conan and other combo based hack and slash games.
You have to slay Legion to liberate parts of a huge island and therefore free vikings to join your army.
When enough are freed and you fulfil various other requirements you can attack the main stronhold in an army vs army battle (you still remain on foot).
Also there are a few dragons you can the favour of who attack selected targets on the battlefield in exchange for runes which you get for killing sub-bosses.
It is good fun but not the best game I have ever played.
I'd give it a 7/10 but remember, there is no MP at all and no DLC is planned so what you buy is all you get...