It's a nice experience, the trolley itself is a good way to get to know San Diego's main spots. The drivers are all very nice, that's the best part of the tour. As they drive they explain every spot you pass along, sometimes history stuff, sometimes they throw in a joke etc. All in all a pleasant experience.
The reason I don't give a 5 star review is for two reasons, one is that the day I used the trolley it was really crowded (I think it was a Sunday), I actually started having anxiety on whether we would find a place to sit down. If the trolley is full you have to wait for the next one and it might take 15 minutes, the thing is that even the next trolley might be full. I heard some people claim they had been waiting over an hour in the hotel stop, the driver later said that was not possible that they were exagerating, who knows but I do know a lot of people couldn't get into the trolley when I rode it. For whatever reason most people didn't hop off anywhere, they kept their seat for many stops, so that made the situation worse, I guess they just cared about the guided tour itself?
The other reason I don't give 5 stars is because of the price-value. We were two people and I thought the trolley would be a cost effective way to get around, but after that day I realized that if I had used Uber it would have been a bit cheaper to get to the same places. Granted I didn't hop off in every single spot of the tour, but then again there is no time to do that. If you are three or four people I would suggest to better stick to ride sharing, it's far cheaper. If pricing is not your concern then yes I would say to use the Trolley just because of the experience of going on a guided tour. Though still there is the issue of seating, I don't know if it was just the day I went but it was frustrating to constantly wait in a line and then hope that someone will hop off the bus at that stop.