We had several pleasant rides with no problems
I can see how the trolleys might not be a good idea during peak season, as there are not many seats (maybe 40?) aboard. Only two people can fit in each seat. We had no problem finding seats as we visited in February. We took reviewers' advice, and started by riding the full tour - that way we could mark where the stops are and not worry about being able to catch another trolley if we "hopped" off. We wanted to see sights we might not have time to walk to, anyway, in addition to getting the commentary.
We encountered several drivers during our three days. All were patient, polite, pleasant, and gave not only commentary, but suggestions, directions, and advice to tourists. A couple of the drivers picked us up or dropped us off when we were not quite at a scheduled stop (where they were able to).
On Saturday, the trolleys ran pretty often, more frequently than every 1/2 hour. We not only took the full tour, but were able to use the trolley the next day to get us to spots that were too distant to walk with small children. We would normally have found the ticket price pretty steep for just a one-time tour ride, but since we got three days through the online deal, and were able to use it for more than just one trip around the loop, I think it was worth it. I do wish they would run later than 5:30, so you could take the tour after the museums have closed. There is a moonlight tour, but that is a separate ticket price. It would be difficult to use it to hop on and off during just one day, as you have to wait each time for another trolley to come, and you only have until 5:30.
All in all, we were pleased with the Old Town Trolley tours. I can see how they might be less than satisfactory in the more popular months, due to overcrowding and traffic, and hot weather testing everyone's patience.