There is no flap over the zipper and the zipper is NOT waterproof.  If you're out in heavy rain for a few hours, you'll end up with a wet line down your shirt from where water soaked through the zipper on this jacket.  If you'll only go out in light rain, or only for short times, the jacket will probably be fine for you.

This is a nice light weight rain jacket and it packs down very small.