I think there's still a good bit of exploring to do even with the linear route, finding chests, secret places, etc, and when you get the airship too you can find a few different places.

I think it's just the way the story runs, and because of Yuna's pilgramage, she has to go to certain temples to get those aeons, I don't think it would run so well if you could just wander anywhere.

Yeah it is a bit movie-ish but I just found it so much fun, hope you do too, just give it a chance anyways