Oh, dear, I imagine Brock wouldn't be much fun with a Pikachu for a starter. I'm trying to think of a good Brock-beater that can be caught before Pewter City, and none is coming to mind. (Of course, the real sufferers are the ones who pick Charmander in Red or Blue, then find themselves completely helpless against both Brock and Misty.)

My fairly limited post-first-generation knowledge largely comes from wandering around on Bulbapedia, which I probably should not find as endlessly fascinating as I do.