Short and sweet: Viking could've been great. The massive battles are a neat idea, the world can seem huge, and while simplistic, the hack-and-slash gameplay is fun for a while. Sadly, the problems in the game make sure that none of those good things can standout too proudly. The battles stumble thanks to chug, the worlds get repetitive, and when you're not really interested in the story or your ultimate goal, hack-and-slash gets on your nerves no matter how many times you cut a guy in two.
There's still content here to like and enjoy, but IGN would suggest sifting through it on the weekend as a rental.