As I learned from the book, the two principals of Sam's Strip were eventually modified and reused as the leads of Sam & Silo, which has apparently been running since 1977 (I think the most recent Sam & Silo I've seen is from 1979 - it hasn't been popular in this part of the globe for decades).
Sam's Strip (created principally by Dumas) was a little too high-concept. The cast of the strip were not only aware of their nature as comic strip characters, but would devote their panels (and gutters) to explaining how their comic strip reality functioned, or satirized old comic strip tropes; characters from comic strips stretching back the Yellow Kid would frequently appear (Happy Hooligan becomes a semi-regular), never quoting the proper ownership copyrights (even with Disney characters). Put most succinctly, Sam's Strip was "meta."
It seems appropriate for such an abstract strip to feature a similarly abstract character and setting. Sam is represented by a giant oval, his head, arms and legs only minor accessories; Sam's surroundings are usually an empty void; it works brilliantly to get across how different Sam's Strip is from other strips on the page.
Does the failure of Sam's Strip suggest audiences aren't interested in "meta" commentary about their comic strips? Not necessarily - "meta" humour frequently appears in (to involve a different medium) Warner's Looney Tunes cartoons; the difference being, the Warner cartoons include "meta" jokes against some semblance of plot; there is no plot in Sam's Strip and it could be why audiences were lukewarm. When the book wasn't being "meta," it devoted itself to many of the same gags and topical humour found in other strips of the day.
My favourite aspect of Sam's Strip are the many guest stars - not simply their presence in the strips, but the care Dumas devoted to capturing each character's style. It's no small thing to see characters like Popeye, Donald Duck and Jiggs sharing a panel, each looking authentic. Although Dumas seldom worked on his backgrounds, when he did, he proved capable of beautifully detailed work (some samples of Sam & Silo provided in the book demonstrate he's still game).
My tiny library of comic strip books continues to grow; my copy of Sam's Strip: the Comic About Comics is a welcome addition!