I'm an SF native and have taken college and family friends here multiple times in the past 5 years. The timeliness, organization, and quality of the self-guided tours and discussions with tour guides has not changed in all these years. I really enjoy seeing my friends and family start to get excited during the ferry ride over (if you don't have time for a bay cruise, this will be a pleasant 15 min ferry ride to and from the island). Each time, they've told me this has been a highlight of their trips.
Once on the island, the exhibits you can walk into on the way to the prison are a nice treat. Once you reach the top, the self-guided tour has a very streamlined process, with minimal lines. While this is my third visit, I didn't get bored. I enjoyed wandering around and getting some great views and pictures of San Francisco and getting a reminder of some very interesting history. If you're lucky, there'll be zero wind and fog.
Bring your walking shoes, a camera, layers, and a water bottle. We purchased food on the ferry ride back to SF since there was no food on Alcatraz itself.
Highlights: walking into prison cells, beautiful views of the bay, overall very well-organized tour, helpful staff, met a former prisoner (he was on the island for the day signing books)