The Lobster Claw on Route 6A in Orleans is a popular seafood place. Really good fried clams the one time I was there. They should have all the usual fare. The Raw Bar in Mashpee is also worth investigating - they are supposed to have great lobster rolls. That's kind of far from Orleans, though. The Lobster Pot in Provincetown is a pretty well-known and regarded place (I have not been.) They have a website - http://www.ptownlobsterpot.com
- so you can look for yourself. Provincetown in the summer can be a bit of an ordeal, but it's still an amazing place.
I'm afraid I don't know the Cape that well - perhaps others can be of more assistance. I'm sure that if you're willing to spend for it, you can get some great food on the cape.