This is one of my favorite places to go in the Farmington Valley area. There's tons of walking trails, a small playground, picnic tables, some with coverage from the sun, and lots and lots of sports fields, aka, wide open spaces. On the property is a small lake (or maybe it's just a pond?) you can go canoeing or kayaking in, and I'm not sure how the fishing is, but I've seen plenty of people having a go at it. Fisher Meadows is a great place to spend an afternoon, alone or with a group- there's pretty much something here for everyone.
Located right near Route 10, on Old Farms Road in Avon, it's adjacent to the Farmington River, and even has a few trails which will lead you to it. It's officially open from dawn to dusk, though the town of Avon website says that, with permission, you can use the property for camping as well! Check it out if you get the chance- here's some pics from my most recent walk around the pond, where I saw a snapping turtle laying her eggs!! She let me get REALLY close to her- I guess she was too preoccupied with the task at hand to chase me away :)