Grandpa's is definitely a classic! Seems like it doesn't receive as much traffic as it warrants. Perhaps b/c it is a wee bit run-out on the upper section;) And yes, the initial moves off the deck are spicy and technical for 5.9. Like Steve says, there was rock exfoliation which changed the character significantly at the beginning. So in its current state, those moves are likely 10b-ish?
I've definitely climbed Grandpa's within the last five years; when I was cleaning and bolting "Let Freedom Ring" (another must do), I couldn't resist revisiting Grandpa's. Although the gear is good and bolts where ya need 'em, I find the climb to be psychologically demanding, and consequently all the more satisfying to send!