Unless you're in the drug trade and/or go looking for trouble, this part of Mexico is probably safer than your home town. Of course, it's not a totally crime free utopia, but so long as you use your common sense, you'll be fine.
As for the water, all resorts use purified water, so it's perfectly safe but since it may contain harmless minerals etc. that your body isn't used to, it can cause tummy upsets. For drinking, it's best to stick with bottled water. If you're really concerned, you can use bottled water to brush your teeth too.
AI food can be mediocre .... but it doesn't have to be. As with most things in life, you get what you pay for and if you want decent food, you're going to have to go for a higher end AI.
If you don't like high rises, then steer clear of Cancun and head further south to the Riviera Maya region. If you want to have easy access to lots of bars, restaurants and clubs, then I'd recommend you stay in, or very close, to Playa del Carmen. Two adult only AI resorts that would fit the bill would be the Royal Playa del Carmen and the Royal Hideaway. I think the food and beach are better at the latter but the RPDC has a better location with respect to access to PdC.
If you want to go non AI (and get the most out of the restaurants in PdC), then look at the El Taj condos.
If you plan on spending most of your time at the resort and don't mind a more remote locale, then there are many to choose from (all of these are adult only, all inclusive resorts):
Secrets Silversands - nice beach for lounging and walking, not so great for swimming;
Valentin Imperial Maya
Secrets Maroma Beach
El Dorado Maroma
Blue Diamond by Bluebay
Paradisus Playa del Carmen La Perla.
There's also Grand Velas, not adult only but probably one of the nicest, high end AI resorts in the area. If you don't want AI, then there's the Fairmont Mayakoba and the Rosewood Mayakoba. These are all at a high price point.
Just an FYI for future reference - it's hugely helpful if you can give a per night accommodation budget when asking for resort recommendations. The resorts I've mentioned are slightly above mid-range price and up. Adult only resorts tend to be a bit more expensive than non AO. If every resort I've mentioned is out of your budget, then check out the Rius in Playacar - great beaches and easy access to PdC.
Edited: 11:15 am, June 06, 2013