This question is in regard to the production values of the show and how believable the sets were. I for one think Gilligan's Island was a fully immersive experience and I was able to believe the scenes took place in the jungle, by the lagoon, etc. on an uncharted tropical island. This is thanks to the set designers for paying so much attention to detail. On every other show I would think, "yep, these scenes are obviously shot on a stage set" but that's definitely not the case here. The sets are so complete, so full of extra greenery, props, little details, and so on. Does anyone else feel that way?

I do know that some of the very earliest episodes actually had some scenes filmed on an actual coastline and in later episodes the lagoon scenes were shot just outside the studio. This in combination with the indoor sets (the jungle, the huts, etc.) made for a very unique show for its time.

I also think the mood of the show was helped in no small part by the incidental music. In all three seasons the music was great and very fitting in creating an island atmosphere. John Williams, Gerald Fried, and Morton Stevens by no coincidence are some of the greatest composers in history.

I too think the overall feel was quite good, especially for the time period and I doubt the show had the world's largest budget. The outdoor lagoon was convincing. The indoor sets were well done and probably helped by the fact that the viewer mostly saw jungle. But, even the "cliffhanger" scenes with literal cliffs, with fake sky in the background, were well handled. They could have done more with breezes and the sound of birds or waves against the shore, but those could have been consciously omitted so as not to distract from the plot and comedy. The talented permances of the castaways' actors, even with the show's inherent silliness, were also convincing that they were on an island. Heck, some viewers believed the scenario as fact, not fiction!

I often wish they would release a CD of the scores for the episodes. I would snap it up in a trice.

I too think the overall feel was quite good, especially for the time period and I doubt the show had the world's largest budget. The outdoor lagoon was convincing. The indoor sets were well done and probably helped by the fact that the viewer mostly saw jungle. But, even the "cliffhanger" scenes with literal cliffs, with fake sky in the background, were well handled. They could have done more with breezes and the sound of birds or waves against the shore, but those could have been consciously omitted so as not to distract from the plot and comedy. The talented permances of the castaways' actors, even with the show's inherent silliness, were also convincing that they were on an island. Heck, some viewers believed the scenario as fact, not fiction!
That's true! I forgot about that story of the gullible viewers. The sets were very convincing. As for more ambient noises, I think they were, as you said, a conscious omission. I remember in some early episodes (when they were still filming some shots on an actual coast) apparently the waves crashing was so loud the actors had to go back and re-dub the lines in a somewhat awkward way.

I often wish they would release a CD of the scores for the episodes. I would snap it up in a trice.
Agreed. The musical scores were so rich and full and I'd love to have extended cuts of them.

The only thing I didn't believe was real was that giant spider.

I complete agree that the sets were realistic, at least enough so that you could suspend disbelief. It really shows what one can do with creativity and ingenuity, even on what was surely a shoestring budget.