Incredible, especially in the summertime. I always feel like I can get better quality produce here cheaper than in the store. The vendors are usually very nice and helpful, and there is always something interesting to try. Bring cash - they don't take credit cards.
If you haven't been to many farmers markets before, this is not one where you can buy a lot of ready-to-eat food - it is mostly produce and flowers. However, if you want a delicious pie, I recommend the Amish tent.