"The Core" meets "Crack in the World" (1965 made for TV). The acting is stock, the suspense predictable. Once you subtract all of the plot ripped off from "The Core" - basically the manned drilling machine - you end up with the plot of "Crack in the World". "Crack" was a truly excellent movie starring Dana Andrews. His team of scientists, working in South Africa, drilled down to the crust and "punched through" with a nuclear device in order to provide a steady source of geothermic energy. One of his subordinates, also a brilliant scientist disagrees. He believes that the blast will not drill a simple hole, but will instead form cracks in the crust. (Possible spoiler) He is right. In order to stop the resultant crack from destroying the earth they must place another nuclear device in the path of the crack.
Although I have placed a spoiler warning, i don't know if I really spoiled anything for either movie. And since "Crack in the World is only available in very rare VHS format if at all my decision not to reveal whether or not the counter-blast works is probably academic.
All in all, I rate "Descent' just below average.