Lafayette is an incredible small city across the bay from San Francisco. It is tucked in between many small parks that are very fun to spend time in, no matter what time of year it is. The Lafayette Reservoir Recreation Area is definitely the best area in Lafayette. If you are looking for a calm, friendly city than Lafayette will serve you very well.
I've been living in Lafayette for a while now and hope to never move away. Yes, it's a very expensive area to live in even by California standards but it's worth it. There are a lot of startups in the area which is great for recent grads or people looking to branch out on their own. It's also a very safe city which is a big plus.
The downtown area has a decent amount of stores and restaurants to choose from, so you probably won't have to go to far to get what you need. Overall, it's a great city for people of every age.