Parks are recreational areas; unfortunately, different people have different ideas of what recreation means - to some that is kids playing, and others think it means drugs and prostitution. Figure out what types of activities are actually transpiring in that park first.
If crime isn't an issue it seems like a good idea. My sister lives across the street from a park. Great view from her front porch and she can watch her kids play from the house. It is definitely desirable in her case as people have asked her to call when she is ready to sell.
As others have indicated, it depends on the types of recreation taking place in the park.
I am presently considering a property whose backyard opens onto a City playground. The property is in "Universityville", but they playground could make it attractive to mature students, or new lecturers/professors, with young children.