I've been to MB twice and the beach area is awesome! MB doesn't have the fabulous "themeing" that Disney does, but if you're in Las Vegas, that's the place to be.
MB's 11-acre water park has a lazy river and a wave pool.
The lazy river is small but has a good strong current. What put me off is that they charge for the use of inner tubes. My immediate reaction was an indignant, "They don't at Disney!" My DH reminded me that the casino really wants you to be inside gambling so they're going to penalize you whenever you're not.
The huge wave pool, on the other hand, is as good as if not better than those at Typhoon Lagoon and Blizzard Beach. (I'm such a die-hard Disney fan I can't believe I just said that!) The water temperature is great and the waves are excellent (powerful enough to give you a good push without beating you up).
There's a hot, sandy beach so be sure to bring swim shoes along. And if you want a drink you simply raise the flag on your lounge chair and a waiter or waitress will seek you out.