Ages of Thunder collects what were once four single issues. The first three, Ages of Fire, Reign of Blood, and Man of War, retell Norse mythology with the Marvel version of the gods. Mostly, it's a series of short myths that all feature Thor, and end with Thor's banishment to Midgard. I have to say, Fraction really nailed the style of a teller of epic tales here. One could very easily read these issues over a flagon of mead, pausing to quaff at key moments. Granted, I'm not as familiar with the Norse pantheon as I am with the Greek, but I really like what was done here.
The final issue, the God-Sized Special (heh) doesn't connect at all. And you would really need to read at least Straczynski's [b:Thor, Vol. 1|2336407|Thor, Vol. 1|J. Michael Straczynski|http://d.gr-assets.com/books/1328050778s/2336407.jpg|2343086] to understand why, amongst other things, Loki is now a woman. It's a decent enough story, but it really pales in comparison to what went before. Besides, the more conventional storytelling style makes for a bit of a jarring contrast. My guess is that Marvel really wanted to collect Ages of Fire, Reign of Blood, and Man of War, but were leery about putting out a three issue collection. I have to say, I'm really glad we got those in a trade, so I can't complain about the extra story.