The big caveat is that you have to walk a little ways from the parking lot. If you have littles, you may want to bring a stroller or a wagon for the path down to the lake and play structure.
This park has a really nice beach on Lake Sammamish. In the summer there is a lifeguard and everyone enjoys swimming in the lake. My kids love playing in the sand all year round.
The play structure is large and has multiple parts for different ages of kids. There is a very large grassy area for playing. There are lots of picnic tables and of course there are bathrooms.
Here is the link to the Redmond Parks site for this park.