I actually found the idea of having "optional" caves, rather than "oh, I need to go through, so why not explore the whole thing anyway" really exciting.
Dark Cave, Mount Mortar, Seafoam Islands (you could go back after the gym), Mount Moon, Cliff Cave....I found exploring them at my own leisure really.
However, Route 38/39 has music which makes it feel more exciting, as do Routes 26,27, Victory Road and the Pokemon League. Oh, and the silence with just the wind, whilst battling Red, is pretty awesome too.
I do find Kanto kinda slow, as there's less of a plotline. However, getting to battle Silver, Blue, and Red, keeps me going onwards towards the Power Plant....