Does the park compliment the desired lifestyle of the buyer? The work at home professional who needs quiet for concentration or business phone calls will not find the boisterous laughter of children pleasant. to another, that sound may be music for the soul.
This is but only one perfect example of why Zillow and the like can never accurately define vaule from a computer thousands of miles away.
Of course if it is well kept, low traffic, and a peaceful place to walk or play, then it could be a bonus.
I agree that it depends on the neighborhood. Before I became a home owner, I thought it would be an idealic setting for raising children etc.
However, I opt for a little distance now rather than closer. Picnics, events, and parties (big ones with megaphones & lots of vehicular traffice) are not my cup of tea. I don't mind attending - I just don't want all that activity in my front yard...
So - I would say in the long run, when it comes time to sell your home years down the road and these problems manifest over time to be "major" I believe the value to the home would be in the negative.