I only did a short part of this trip, but it was worth while and the tour guide was very helpful.
I've toured DC many times before at a more leasure pase, but this tour was not that great. We flew by the major sights from a far distance so couldn't take photos unless we were lucky enough to catch a red light. They tried to cram too much into the tour, more quantity than quality.
When we got off one time and couldn't figure out where to catch it again and had to walk several blocks back to the welcome center. Also the Welcome Center where we caught the trolley was not in the best location for visitors, right in the middle of busy downtown traffic, had to circle at least three or more times before realizing the parking garage was the only place to park long term. My worst experience while in DC.
Excellent tour of D.C. and area; allows you to see and learn information about all major places, monuments, buildings, etc. So easy to hop on and off to see places of interest. The trolley is always on time for your convenience. Great information provided by guides. Was able to see all major sites, even Arlington National Cemetery. So glad we used Hop-on-Hop-off!