Yank Sing has consistently good dishes.
Koi Palace is so-so. I once had deep fried crab claws that were so big the meat was still raw in the center of the thing -- I thought it was a one time mistake but a second go at it had the same rawness. I don't like oversized food (golf ball sized wontons, for example) and this is a reason why.
There is a newish place Hong Kong Lounge II on Geary and Parker(? where the old Straits Cafe was) that served up pretty good dishes the one time I was there. The place is small though.
The Kitchen in Millbrae was a serious disappointment. Their dumpling were all over steamed and "broken". This was over a weekend. I've had better on a weekday.
You mentioned oysters. There is one place you must NOT go: Skool. They have cheap oysters but everything there is bland and very disappointing. Their lamb dish was devoid of muttony flavours. A friend thought it tasted like pork. To take mutton and turned it into mystery meat is a feat. On second thoughst, maybe you should try it for the novelty of what an over-priced restaurant should not be. I went there fooled by their 5-star reviews on Yelp.