Beginning with #11, the Beast from the X-Men would take over the title. This was his first appearance in his 'furry,' monstrous form, and subsequently the issue has become popular with collectors (and, thus,expensive). The Beast would stay in the title through #17, with frequent guest-appearances by the X-Men themselves.
A new storyline began in #18, unrelated to Marvel's larger superhero universe. Creator Roy Thomas took the idea of H.G. Wells's novel War of the Worlds and postulated a re-invasion of Earth by the globular, tentacled Martians in the early 21st century. Taking most Earthmen into slavery, the Martians patrol the blasted planet with their tripods, robots, and mutated humans; they are finally opposed when one man stands up to face them - a trained gladiator called Killraven. The adventures of Killraven and his followers was an odd melange of different elements, combining almost-superheroics with sci-fi and sword-and-sorcery. Early stories moved a bit too briskly, as the characters careened from battle to battle; as the series wore on, however, the storyline became more comfortable with itself and began to proceed more naturally.
Issue #38 featured nightmarish versions of Marvel's most popular superheroes on the cover. If this were a ploy to entice new readers to pick up the series, it should have been done earlier - because the next issue was this title's last.
You can see a gallery of Amazing Adventures covers by going here.