Up until two months ago, I lived in apartments next door to El Diablo on Queen Anne, and I would go there every morning to buy coffee on my way to work. The staff were polite and friendly, and seemed to know every customer who came in the door. It felt as if I had a special relationship with the staff. For example, I ordered a Mexican mocha on a regular basis, the chocolate/coffee/cinammon/spice beverage. In time, they figured out that I was in it for the kick, and offered me a cayenne mocha. It wasn't on the menu (they will give it to you if you ask) --- it tastes like a chocolate covered red hot. It was nice that they would think about what I would specifically like, and touches like that made me feel welcome.
El Diablo wasn't only a place to get that morning caffeine fix. If guests were visiting, I would take them over to brag about my neighborhood. The other reviews detail the heaven/hell combination, but my favorite part to show off was the cakes and tartes. El Diablo contracts through a number of bakers, and are quite discriminating over what they pick. I've seen interesting combinations, including a mojito lime tarte that was delicious. We'd get our orders and sit down on the comfortable couches and chat, and felt no pressure to leave.
In the evening, local musicians would perform, and the crowd seemed to enjoy the place. The coffeeshop serves meets multiple needs -- it is a community hangout. You don't just go there for the coffee (but if you did, I wouldn't fault you). You go there for the atmosphere.