I have been shooting Terroir Coffee's Grand Cru Kenya: Mamuto, Kirinyaga. Really nice flavors in the mouth. There's a bright acidity, and berry flavors, but I don't find it to be too much. It makes your cheeks pucker a bit, sort of like eating sour patch kids, but not in the front of your mouth, more toward the back of your tongue. Because it's so lightly roasted, there's no burnt rubber taste you'd normally associate with offerings from Starbucks or Peet's.
Single origin espresso is not for everyone. Coffee Review's Ken Davids, who is the closest the coffee industry has to the wine industry's Robert Parker, said in his review of single origin espressos last month: "The results clearly suggest that there may indeed be a trade-off with single-origin espressos: Most of those we tested clearly displayed less balance and depth of sensation than a good blend. In compensation, however, they also offered opportunities for recognition, for sensory exploration, for surprise, for the very kind of dialogue with nature and culture that blends with their usually secretive formulas tend to obscure."
I like them because it's so radically different from what "normal" espresso tastes like, and I enjoy making it for friends to see their reaction. Again, you typically get lighter roasts from single origin coffees, and when you shoot them, the acidity shines through the cup, as well as some interesting flavors you don't expect in coffee. If single origin coffee has clear hints of citrus or floral flavors, making an espresso with the same coffee beans turns the dial up. Instead of thinking to yourself, "hmm, I think I taste lemon in this coffee," as an espresso you feel like the lemon is smeared all over your tongue.
So while this may not be of interest to everyone, and when you combine that with milk, may be a little weird, I think it's just exciting to take these beans and see what shows up in the espresso cup.