This book includes three issues of the current Thor run, an issue of Thor Annual (a periodic collection of one-shot stories) and a What If? story from forty years ago (a story outside of the normal Marvel timeline). Unfortunately, despite the buffet of options, this collection features little thriller and a lot of filler. I’m disappointed that Marvel would put out a trade with only a few lackluster issues and then slap in some random Thor comics in the back. However, I did think that the short stories from Thor Annual included this book were much more interesting than the issues of the current Thor run collected here. So maybe there’s some wisdom in throwing a lot on the wall. 
Who Holds the Hammer? picks up where Goddess of Thunder (which I loved) left off. Malekith and an oil company executive are up to no good. Odinson (the god formerly called Thor) still doesn’t know who the new Thor is, and Odin is a grumpy old man complaining about how things were back in his day. I loved that the first trade didn’t reveal who Thor was, just like how season one of Twin Peaks didn’t reveal who killed Laura Palmer. This book does reveal Thor’s secret identity, which lets some of the air out of the Bifrost tires. However, it’s a well-done reveal and the best part of the book.
Thor Annual 1, which is included here, contains three one-shot stories within itself. They are of varying quality, but the art by Marguerite Sauvage is noteworthy. It looks like a cartoon from the 1970s in the best way possible. If you like the DC/Hanna-Barbera crossover art, this is even similar but more fantastical. Former pro-wrestler CM Punk also pens a story, which is fun.
The included What If? Issue doesn’t age well in my opinion – it’s cluttered and the story is kind of silly. While I grew up on comics from the ’60s through the ’90s, somtimes I think it’s better to leave the past in the past.
I won’t be adding this book to my library. The e-version of the comic I linked to is only $1.50, though, so if you want to keep up with the story it’s a modest investment.