I hadn't been back to San Diego in over 10 years, but the city is still a pleasant place to visit. I was only there about a day so didn't get to the zoo this trip, but a couple a high points you shouldn't miss.
1) The waterfront is a lot of fun, in particular, the new USS Midway. She is docked right at the waterfront (Harbor Drive and Broadway) and is amazing. Millions have been spent refurbishing here, so plan to spend several hours wandering all over her, listen to the volunteers talk about life aboard the ship, carrier landings, see the planes and helicopters on the flight deck and then grab a snack and take in the harbor. The ship is massive, but has ample benches and elevators for those needing special assistance. Kids will eat it up.
2) Other place I enjoyed is the Seaport Village. It's loaded with stores for shopping, stands for food and restaurants. Clean, nice and great view of San Diego bay. A great afternoon.
3) If you like to talk walks or run, the harbor has a great path that hugs Harbor Drive. I did a seven mile run there early one morning and it was wonderful. Go down Broadway to the bay and you run right into Harbor Drive.
The one thing to get ready for as you venture out, though, is the homeless population. With such a nice climate they are everywhere - city streets, parks, bus/train stations, the harbor and lakefront paths. I grew up in Philadelphia and now reside in Chicago so nothing new to me, but be prepared if you aren't used to this or have young children. The homeless are not hostile like NYC, but you need to be mindful of your personal security, particularly after dark if you are walking alone.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.