Ultimate Comics: Thor is written by Fantastic Four scribe Jonathan Hickman with art by Carlos Pacheco. It collects all four issues of Ultimate Comics: Thor with a few extras. There are three main stories told throughout these issues. The first is Thor's younger years in Asgard, Ragnarok, and a prequel to The Ultimates: Ultimate Collection. Pacheco's art is adequate enough for this series. People look how they should, environments are accurate, and the colouring is good. Hickman nails dialogue and characterisation for all his characters.
The subplot involving the definitive origin of Ultimate Thor is interesting. It's essentially a tale about the Frost Giants trying to destroy Asgard and Loki (inevitably) betraying everyone. The second subplot involves Baron Zemo launching an assault on Asgard. This event is Ragnarok. It is much more interesting and had a few surprises. The final subplot is about Thor being held in an insane asylum a few years before the events of the Ultimates. Brian and James Braddock make appearances along with Dr. Donald Blake.
Hickman manages to weave together these three subplots to create one great story. There's a few surprises where I went, "Why didn't I see that?" Overall this is a fantastic read for any Ultimate Thor fans and will answer a few questions you may have been asking yourself regarding Thor. For more casual comic fans, you may want to pass this up.
I wanted to say more but because it's Hickman, I'd be giving off some major spoilers.