'Cody' has some of Kerouac's finest descriptive passages. Some of the language, the meandering, rollicking lines, the drawn out sketches, are utterly brilliant.
But I was never captivated by the stoned babbling transcriptions.
I suggest reading 'Cody' in bits and pieces. Sit down, open it up 'til something catches your eye, and read until it bores you or something else comes up.
As for 'Dharma Bums' - definitely read it. Cover to cover.