Even pre-Gen 3 any route that's primarily water was pretty bad. Just a big wide expanse of mostly nothing. Maybe you'll find a cave if you don't get annoyed by all the Tentacools and battles with Water Pokémon trainers first.Third-gen Pokemon games trade the varied forest/mountains-volcano/desert in the beginning of the game for open ocean. They're going for a balance between land environments and water environments to reflect the Groudon/Kyogre conflict, but man, all that water is pretty tiresome to surf over.
That said, I did like how the Hoenn generation had underwater maps. I'm sad the later generations didn't expand on the underwater exploration.