I think the most exiting thing that can happen when dry fly fishing is when you see the trout coming up to take your fly. The last say I was out fishing on the Kelvin I was casting downstream to a trout that I had seen rise, I was getting a drift of just a few feet and suddenly I seen a flash as a brownie rose up from the depths of the pool to take the fly, it came up like a rising torpedo. Just at the last moment it turned away as suddenly the fly started to drag across the surface. I cast again but this time the trout took and was certainly not a happy chappy as it was jumping out the water and generally raging that it snack was a bit of tomfoolery. The same thing happened when I caught my first big trout from the Kelvin.
Exiting, you betcha