This is my favorite Vietnamese place in the valley and I've been to tons. Their pho broth has a really good flavor and the herbs/greens that come with their meal are crisp/fresh. Their spring rolls are really good. Most people serve it with hoisin sauce, but Khai Hoan has a really tasty peanut sauce to go with it. And their pork isn't just sliced cooked pork, theirs is marinated/grilled so it has a nice smoky flavor.
Try the specials. The banh xeo is like a crepe/omelette and you get 2 huge ones in an order (I only got one when I got take out though....) and the other special (who knows the name), is a fish cake noodle soup that's pretty good too.
Owner is friendly and service is efficient.