It's not bitter. It's not sour. I really don't know what else to say. Today, after dialing down my mill a bit (it dialed down more than I expected to be able, and still has some room), I pulled two shots. I can't complain about either. I finally have tasted one that verifies what I've heard over and over, that espresso is not bitter.
Both shots were about 25 seconds and yielded just over 2 oz plus crema. The first one was unremarkable from my perspective (that's good, since all have been sour up to this point). But the second one really seemed somehow balanced. It's such a new experience for me that I really didn't know where to go with my observations. I'm sure it can be dialed in better, so here are some pix for both celebration and correction.
First shot - Columbian
Second shot - Monkey Blend
Thanks to all who patiently walked me up to this point. For me this was a milestone and is kinda exciting. And, of course, any further critiquing is encouraged.