I think one of the things I like most about Harry Stubbs is that he's a character we wouldn't normally get to hear from: the hired muscle; an ex-boxer; a henchman who gets called on when things get confrontational. Most stories like this would be told from the perspective of Skinner, his pal, with the lumbering heavy reduced to a 2D caricature. It's very refreshing to be told things from the perspective of the bodyguard and enforcer, and a welcome departure from the ruthless averaging, common to too much fiction, per which anyone with physical skills must be a lunkhead, and anyone with insight or knowledge must be a bit of a weed.
Which isn't to say Stubbs is omniscient or infallible--far from it. He spends most of this story playing catch-up, tussling with anomalies and puzzles which will also intrigue the reader. Hambling plays his cards close to his chest, and even those with a good background knowledge of the Mythos will take a while to figure out what's going on. As other reviewers have noted, it eventually becomes apparent that the Mythos background to Alien Stars lies in an HPL story that has been rather under-utilised by contemporary writers, and is all the more welcome for that.
Another reason I like the Stubbs stories is that the protagonist isn't trapped in amber: he changes jobs and circumstances, maintains relationships with characters from previous books, and develops throughout the series. This time, for the first time, there is even a tantalising hint of romance in the air for Harry. This is offset against the action, which is more frequent here than in the previous novels, particularly as the story reaches its macabre and violent climax.
Overall, a very satisfactory third outing for Harry and friends. These books deserve to be read (or listened to, for the audiobookers) in sequence, but when you get to this one you can be sure you'll enjoy it as much as the previous two--I certainly did.