Walpole Park has a lot going for it. It's only a few minutes from Ealing Broadway station and the shopping areas.
It's a good size, and can easily accommodate several football matches while leaving room for picnickers. It has duck ponds, open grassy areas, trees and shrubs, a small gazebo, a (quite busy) young children's playground, lots of benches, and a really nice pond with some small bridges (the latter area often used for wedding photos). There are flower beds here and there, but mostly you just feel it's lawn and bushes and trees.
It's well-kept, and I see constant renovation to keep it up (new trash bins and benches are being put in).
Come here on any sunny weekend and you'll see families having lunch, people feeding the ducks and squirrels, playing football and frisbee, and people running.
I use this park all the time for running. The paved path around the perimeter is almost exactly 1 mile in length (as is Lammas Park, which is just across the street on the south side of Walpole).
The Ealing Summer Festival (http://www.ealing.gov.uk/services/leisure/ealing_summer/) uses Walpole Park a lot. The Comedy Festival and the Jazz Festival both set up here for a week each. It's a great place to hold large-scale tented events, and miraculously the grass comes back every year!
The London Wildcare Field Centre was opened here a couple of years ago, which rehabilitates injured urban animals. Kids can see birds, foxes, and other animals here and learn a bit about them. I see a lot of animals in the park anyway: many birds and squirrels and ducks, and even cranes in the pond by the bridge.
Pitshanger Manor is in the park, a beautiful historic home with a free art gallery inside, open 6 days/week.
Walpole Park is open 7 days a week, but, like most, its hours vary according to the time of year. It's roughly open when it's light.
Downside: like any public place, you do sometimes get people drinking and sleeping in the park. In the evening, teens do gather and inhabit it (even after closing). As a result, there is a blanket order that police can order you not to drink in the park, or ask you to leave if you fail to do so. This order's clearly aimed at troublesome and underage drinking, though, and they never bother those just having a quiet picnic. read more