Cinema can be divided into pre-Star Wars and post-Star Wars, especially special effects movies. Harryhausen is no exception. Sinbad and the Eye of the Tiger got lackluster reviews mostly because it was unfavorable compared to Star Wars. Clash of the Titans seemed to be viewed as a quaint folly; entertaining, but without substance. No wonder Harryhausen retired.
I think his unrealized projects would've had to be produced before the Star Wars technical and narrative revolution, but at the same time I can't see how that would've been possible. Harryhausen seemed to always be working. It's a miracle he managed to do all the quality work he did.