Published in 1941, this is Heinlein taking on the challenge of a time travel story, and he does well at it, real well.
The start is good, but Heinlein falls into a writer convention that I find tiresome: If the writer wants the protagonist to do something stupid, especially in the first act, he or she has them drink too much. Yeah, there are enough real world examples that it's believable, but it's tiresome. There are many other ways to do stupid things in the first act. Then again, this is why temperance movements have such strength. It seems there are no universally good solutions to handling human mind altering practices.
Heinlein is quite artful in this story. I wonder how long he took to assemble it? This first act has about five different time threads interacting. It's a masterpiece. The language style is also interesting, lots of word choices that are way, way out of style now. The unliked stranger is a "lug", and I don't think I've heard of a "freshwater college" in any other usage. Interesting that the "if you can't do, teach." attitude is active in this time frame. Bob is getting a PhD to become a college professor because it's good work if you can get it.
Yes indeed! My kind of story: An adventure that is going to reward you with a dozen beautiful, willing women! I wonder if you could get away with this kind of reward in today's woman's rights culture?
Oh my! This is good! I read through the rest in a single sitting. The internal consistency is jaw dropping! Even at this reading I loved it! This is why Heinlein has the reputation he does! He has this protagonist intertwine about five times and never loses it. This is comparable in tightness to Tolkien and Lord of the Rings. It makes me wonder how long he had to spend assembling the concept.
Heinlein mixes in quite a bit of philosophy. I guess that's why the protagonist is a PhD candidate working overtime on a thesis. It's not enough to get in the way of the story, but I don't feel it adds much.
In sum, this story it makes me envious. It is so well crafted! I may have to try my own effort at this.