Out of the three Marvel Masterworks devoted to the Atlas Era of Marvel Heroes this one is the best; so says Roy Thomas in the introduction; and I agree.
This is not to say the other two volumes are bad, but the artwork from Bill Everett, creator of Sub-Mariner is top notch. If there no words in this book you could look at the fantastic illustrations and be entertained; but the stories are fun also. They even have tales of Namor (the Sub-Mariner) when he was young.
The odd thing is his personality changes from story to story. Sometimes he wants to kill the "surface-dwellers" at other times he is friends with us. Such a moody hero. But all in all the stories are like proto-Marvel stories, not as simple as golden age stories can be, and yet not as sophisticated as Marvel would become.
Died too much before his time Joe Maneely provides provides the covers for several of the issues, illustrating a talent that would surely be missed.
Rounding out this volume is some filler stories (pretty amusing); a smattering of golden-age Human Torch and Toro stories, and the forementioned Roy Thomas introduction which gives one a context for these stories.
A very entertaining volume, and this is coming from someone who does not really love the golden-age comics all that much.