Viking Age is a large sourcebook like Avalanche's Celtic age. over 200 pages of real good stuff. Unfortunatley it still had a cheescake cover. But other than that it is the best viking supplement I have seen.
"Ragnarok! Tales of the Norse Gods". is indeed one of the shorter ones. I didn't like either of the short ones, although YMMV. It started with the covers, and then the stuff inside was far to brief.
I did buy Avalanches Celtic Age though and loved it, finding it to have the breadth and depth that Avalanche's shorter products lacked. Then came Viking age, which was similar to Celtic Age in quality and content. It is awesome. A very realistic take on vikings mind you.
Razuur