You'll be surrounded by water you can't swim in (it's passing by at 15-20 knots or so), but all but the smallest ships will have at least one "swimming pool" (perhaps covered, otherwise usable only in warm climes) and deck chairs. The pools won't be great for swimming laps, but some new ships are being equipped with small, swim-against-the-current pools. Most are filled with processed seawater.
Without the legal restrictions imposed on land-based facilities, most cruise ships have a casino except for Disney. Expect more emphasis on gaming on ships catering to Americans than for Europeans. Don't expect table games or machines with payoff rates even close to those found in better land-based casinos; concessionaires must pay dearly for the space. It will be open for gaming only while at sea.