We have a pretty nice one about 2 miles from my house. It's 3 acres fenced, with separate large and small dog areas, and both sides have a few agility obstacles set up. I kinda wish there was a little pond, but at the same time I'm glad there isn't, because Harry luuuuuves water, and he would spend the whole time in the water and I'd have to bring home a soaking wet dog in my car. 
But, because we don't have our yard fenced in yet, which we will be doing this spring, it's an excellent place for Harry to get some decent exercise. We just started going last weekend, because I wanted to wait until at least 3 weeks after his last round of vaccines. He has a blast at the park! Most of the dogs that have been the three times I've been there are wonderful. Only one incident this past Wednesday of an overly aggressive dog that ran into Harry at full speed (on purpose), and knocked him over and he hurt his leg a little. He was fine after a minute or two, and the owner was very apologetic, and right after it happened she leashed her dog and left, which I respected. Just like your child joining a soccer team, there are going to be obnoxious people who ignore the rules, but most folks at my park are pretty cool. I agree that it's a good idea to try it out during off-peak times, or to bring your dog and walk them around outside the fence first a few times. Plenty of folks do that at the park I go to. The dogs inside the fence will run up and sniff them, and bounce around saying "come play with us!" but you know your dog can't get into any trouble that way until you're confident about bringing them inside off leash.