As western high points go, Harney Peak does not present a difficult physical challenge. But the scenery is first rate. From the Sylvan Lake trail head I took trail 4 on the way up. The views of the spires, and needles are spectacular. Amongst the small group I hiked with was a geologist, who pointed out the very diverse geology of the Black Hills region. The expansive views from the summit, including the back side of Mt. Rushmore (no, there are not any presidential "moons") topped off the ascent. I descended on Trail 9, the Harney Peak Summit trail, a more direct approach, but less scenic.
There is a good amount of intermitent shade on both trails, never the less, I would recommend an early start in the summer, as it gets pretty warm by the afternoon. Also, parking is at a premium in the afternoon, as people come to enjoy the picturesque Sylvan Lake. Parking was plentiful in the morning.
I highly recommend this moderate hike.