So much of rewatching the original Star Trek requires filtering for the time period. Most of the time, it’s easy to do. Sometimes it’s a lot harder to get past it.
This is one of the latter. The general storyline is excellent. The notion of alien beings who were worshipped by ancient humans as gods is hardly new—the Marvel Comics character of Thor was built on it prior to this, the entire Stargate franchise will be built on it, and your humble rewatcher has used it as the spine of a cycle of short stories, to name but three of hundreds of examples—but it recurs because it’s a good one. It helps that Michael Forest puts in a bravura performance here, lending regal dignity to a role that absolutely requires it (especially while wearing that hilarious toga).