After 2 years of bringing a whole new audience to Thor, writer J. Michael Straczynski left the title due to the impending "Siege" event coming around the corner at the time. To begin with, JMS got to do 6 issues to his own accord in 2007 to restart Thor, so long as he had complete creative control over the time frame. He ended up doubling that, due to his the success of the newly done Thor title. So around the time "Siege" came knocking around, which meant JMS would lose his control of the Thor storyline because Thor was to star in the "Siege" story by Brian Michael Bendis, JMS wanted to bow out. No animosity, no creative differences...just lose of Thor's storyline. After this, Marvel scrambled about to find a replacement ASAP to fill the void. And who would have it, they found writer Kieron Gillen, and they found a surprisingly good Thor writer.
THOR ULTIMATE COLLECTION collects all of Gillen's run on Thor, including:
Thor: Latverian Prometheus (except Sif #1)
Thor: Siege Aftermath
--Considering each of the links above have a far more detailed review of each story, I won't write out a review detailing each story as much, and I suggest you read each one for better understanding.--
To begin with, Gillen had the difficult chore of picking up JMS's un-concluded ending, then writing the many sub-characters of Asgard during Siege, and then picking up the events for Thor after Siege to lead into Matt Fraction taking over as Thor main writer. That's an utterly difficult task for any writer to deal with, but Gillen manages pretty well. To start with, Gillen writes a convincing Thor. Though he doesn't quite live up to JMS's Thor, Gillen still carries on most of JMS's best features about the cast and characters as well. Thor is still slow and methodical, fairly intelligent and still convincingly powerful (as he should be). Balder and other Norse Gods are still fairly involved and interesting to watch. Loki is still Loki, but Gillen finds a great way of making it where the characters don't fall for his tricks. I'm a bit tired of Loki always getting his way, so seeing Gillen write it where it doesn't always work is beautiful. It should be noted Gillen's Doctor Doom is impressive and menacing to watch. Even if Doom's presence is short in the book, it's good enough to hope for more of Gillen writing the evil doctor in the future.
Of the 3 stories, Latverian Prometheus is must pick-up if you fell in love with JMS's Thor run and were disappointed in the ending of Thor, Vol. 3. It left every reader hanging, but seeing Gillen actually finish JMS's run and add layers to his story arc really is amazing to read. The arc is short though, but well worth reading. Not to mention Latverian Prometheus is out-of-print and costly to buy brand new, so having it here is a real treat. Thor:Siege and Thor:Siege Aftermath are also well written by Gillen and can still be bought in most outlets, but is mild compared to Latverian Prometheus. And because of the average story telling of Thor:Siege and Aftermath, it does bring the collection down.
The negative around the collection is not the writing itself, but the stories. Gillen shows the man can write a good story and compelling characters, but Thor:Siege and Aftermath are "just okay" stories in the long haul. Again, Latverian Prometheus is excellent and the big pick up for the book, but it's short, and it ends JMS's story arc. Thor:Siege has nothing to do with Thor personally and talks about the Asgardians (and a Vostagg story) during the Siege event. It's good if you're interested, but it adds really nothing to the Siege event, so it can be passed on. And Aftermath is mostly a story about Thor going to Hel and clearing up a dispute between Hela and Mephisto fighting over land. It's not a needed story, so it might feel incomprehensible to want to read as well. But again, none of the writing is bad at all. But the last 2 stories don't quite live up to the first story.
The other thing might sound weird, but since all 3 stories are different (as well as the changing art styles), they're written differently to which might not fly with everyone. You would think since Gillen writes every story, they'd have a certain flow or consistency into one another like many other trade paperbacks today, but not here. You might really enjoy Latverian Prometheus, but not like the 2 stories as much. Or you might really like Aftermath, but thought LP and Thor:Siege were not as good. 3 different stories means you might not like all 3 because of the differences. I enjoyed the 3 stories regardless, but again, read the reviews for each book individually to get a feel for what you're in for.
THOR ULTIMATE COLLECTION is pretty good read, especially since this might be Gillen's only time to really shine as Thor main writer (though he is writing the current books of Journey Into Mystery). Even if one story is great while the other two are okay, it's still pretty good to have it in one whole package. If you followed JMS's run, I strongly suggest picking this book up. If you haven't read JMS's run on Thor, and then take caution into buying this collection first. But if you enjoy Gillen's writing, then it's a good lead up to his future writing on Journey Into Mystery: Fear Itself and Journey Into Mystery: Fear Itself Fallout.