I've enjoyed Murray Leinster's short stories, and one thin, light novel. I was surprised to find I enjoyed this story so much. It's a pulp adventure, but it's reasonably well thought out. Calhoun is an ultra-competent hero, but he's unusual in bringing to bear more brain and less brawn than your usual pulp hero, and in the fact that, at heart, he's a determined bureaucrat, not wanna-be soldier.
The Mutant Weapon was originally serialized in Analog, and it shows. There are points of substantial repetition, but it's not hard to skim by. There's also a certain element of 'magic' - Leinster comes up some palatable science, but he also relies pretty heavily on some invented compounds with a striking effectiveness. The plot is not complex, and there's really not much question that Calhoun will prevail, but it's still fun to read.
Ultimately, an unusual, interesting approach to SF adventure. I look forward to the rest of the series.