My ISTP impresses me all the time. Not just with his knowledge and how in touch he is with his physical surroundings, but also his determination and quiet resolution. Funny story: few weeks ago he came over and we were clearing out the shed. Found an adult sized pogo stick that us lot gave up on, having not managed to get a single bounce out of it before falling off. ISTP picks it up and figures he's gonna have a go. Gets two jumps first time. Within 10 minutes, he's got 15 jumps, even though the pogo stick's air compression springy type thing is badly in need of pumping up. Few days later he turns up with a pump, sorts it out, and doggedly stuck at it, in the blazing heat, til he'd done about 30 jumps.
I was so impressed, I joked "Oooh you're sexy when you get all determined!" But for an instant there, I was almost turned
Knowledge is quite hard to impress me with... understanding and insight though, impresses me. And good human qualities like patience, compassion, willpower, kindness and faith (not necessarily in supernatural stuff). And competence.