Great port with Old San Juan, the Moro castle, Casa Blanca, shopping and restaurants. Very atmospheric. Take a taxi or the free shuttle to the top (Moro), then walk back down or pick up the free shuttle at one of several places.
We especially like Coral World aquarium and the adjacent beach. All the taxis are group taxis - more like shuttle buses. But you can get from point A to point B without having a driver wait for you. There are good restaurants downtown, and, of course, lots of shopping. Pastoral St. John's Island is not to be missed.
We saw the botanical garden and the manor house, but had a horrible taxi driver who assured us he would drive gently, then proceeded to use a "shortcut" that involved terribly rutted roads. We talked to him about the problem, but he then took an even longer shortcut on such roads. I feel he was very dishonest.
My low rating is somewhat subjective, as we did not venture beyond the town. We met a very friendly woman preparing spinach for sale at her street-side table, bought cold drinks at a nice courtyard cafe, saw the old slave market, and the "circus" modeled after Picadilly. Friends had a nice tour of the island, and had a positive impression.