The few I've kept are pretty interesting. You'll usually be able to see them poking out from under a rock where they've excavated a den. Will come out to snag food or occassionally explore. I've had the larger pink spotted species which are pretty assertive. Pair it up with the appropriate shrimp and you've got a cool relationship.
very great fish to have. a goby and pistol shrimp is one of the best combos you can have in a fish only or a reef tank. i have kept a yellow watchman and a pink-spotted, both with a tiger pistol shrimp. the larger pink-spotted watchman is more active and protective, but i have really enjoyed them both.