I liked the theme answers today, being a big fan of the PLANETS. The revealer claims that the planets are the etymological origin of the five theme answers (MERCURIAL, VENIAL, MARTIAL, JOVIAL, SATURNINE). I wondered, though, when I finished the puzzle, if saturnine traces its meaning "gloomy" (one definition) to the planet, or to the Roman god Saturn? So, I looked up each of the planetary adjectives in my American Heritage Dictionary and three of the five words did actually refer to the planets themselves and astrology in the definitions, while also referencing the gods. Mercurial and venial did not. The definition of venial didn't even mention Venus, just the Catholic Church and the Latin word venia, forgiveness. Not that my dictionary is the last word, so to speak, but it does introduce some room for debate, not enough that I am not going to moon over it, however. :)
The astrological aspects of the adjectives not withstanding, the planetary descriptors are orbited by a solid set of math and science subject matter including CUBES, UNIT, TRON, PRISM, USENET, MONOMER, EROSION, and SPACE - bonus theme material!
In addition to the full bodied theme answers, I also liked MUDPIES, HUMORME, ONEROUS, and BOAST.
The clues "Clink on the drink" (BRIG) and "How about we forgo that" (LETSNOT) also entertained.
I decided to use VOLGA for today's illustration and suddenly IMALL down a rabbit hole. The Wikipedia article about the Volga included an image called (in English) "Barge Haulers on the Volga" which I found fascinating, so then I had to look up the artist and all his other works, one of which featured Ivan the Terrible with his son, the Tsarevich dying in his arms, so then I had to see what that was all about. Anyhoo, all very interesting, but entirely off SCRIPT vis-à-vis a review of Mr. Eaton-Salners fine puzzle.