Be prepared for a long day, but you get to see SO many different landscapes (city, hills, central valley, mountains, then...oh my...the breathtaking Yosemite Valley). In spite of the hiccups, I would do this again.
We had one couple who was about 20 minutes late arriving to the pick-up point (no big deal). That same couple got lost on the trails while we were in the park and arrived back at the bus about an hour late. Another two group members were about 20 minutes late getting back to the bus after our dinner break. All of this meant we didn't get back to the city until much later than expected.
The one thing we felt was missing was more detailed directions from our guide once we entered the park. We were given park maps and some general guidance....but, we learned a little late that the maps aren't great and the trail signage was minimal. For us, that meant that we weren't able to complete the circuit we had hoped to do (when we realized we weren't where we thought we were on the map, we knew we had to cut our hike short in order to make it back to the bus on time). For the other couple, they were so turned around that they made the whole group an hour late.