By about 1968 Stan Lee had hit the wall as a comic book writer. The titles he still wrote, Fantastic Four, Spider-Man, Captain America, etc were becoming increasingly stale and repetitive. They were still for the most part quite readable but the energy and imagination from the middle years of the '60s were missing.
Fortunately, Lee had brought aboard Roy Thomas to do the writing on some of the "lesser" Marvel titles, like Avengers, Dr. Strange, Sgt. Fury, X-Men, and Sub-Mariner. These titles helped keep Marvel afloat creatively when comic book sales started a precipitous decline in the late '60s.
The Sub-Mariner was never one of my favorite Marvel characters. His problems always seemed largely self-inflicted due to his arrogance and temper making him difficult to sympathize with. I always thought he worked best as the "noble villain" rather than as a "flawed hero". I didn't really think he could carry a title.
The comics in this volume, Sub-Mariner #2-#13 from 1968 and 1969, largely proved me wrong. Thomas sets up an interesting story arc involving a mysterious helmet. But we have plenty of diversions along the way as Namor runs into the inhuman Triton, meets an old enemy Attuma and a new enemy Tiger Shark, picks up some more supporting cast in Diane Arliss and old friend Betty Dean Prentiss, and finally finishes up with Lemuria, Karthon, and Naga.
There are a few missteps along the way. Thomas offers up the obligatory heroes fight each other (Namor and Triton) before combining against the villain (Plant Man). Namor has his usual counter productive and self defeating outbursts of temper. The main plot thread (the helmet) does show signs of being made up as it goes along.
But all in all this is a fast paced 12 issue romp that keeps the reader involved. John Buscema's art is terrific and Gene Colan and Marie Severin do not disappoint either. There is even a bonus parody story from Marvel's humor title Not Brand Echh. Finally, the reproduction is superb.
In short, this is as good a title as Marvel had in the late '60s, with the possible exception of the Avengers. Highly recommended.