Stonehenge is a terrific experience in general. The half-day tour is basically a coach ride up and back. While you’re at the site, you’re pretty much on your own. But during the ride, the tour guide (Darren, in our case) provides commentary in London on the sites you’ll pass and at various points during the ride as well. As we neared “the henge” or “the beautiful stones” as Darren referred to the monument, he gave a lot of interesting commentary on the theories of its creation and purpose. No complaints about Darren - he was great, full of interesting info, and very friendly. But once you get to Stonehenge, it’s not a guided tour. That might be your preference of course, and we enjoyed just walking around and taking in the grandeur of it all. But we wouldn’t have minded some commentary during that walking around either.
The coach ride was comfortable. Be prepared - there are no toilets on the coaches. But there are chargers for your phones, and the seats were pretty comfy.