Fantastic OP! Really covers whats memorable about this game.
I honestly feel GTA V surpasses San Andreas in almost every way. As you pointed out the soundtrack to San Andreas is a masterpiece, and is one area where I feel GTA V came up short. Outside of that, GTA V is a superior game in every other regard.
In all honesty this sounds like nostalgia. The missions in GTA V are way better designed than the missions in San Andreas. I don't remember coming across nearly as many terribly designed missions in GTA V as I did in San Andreas. The chasing the train on the motorcycle one still sticks out in my head as a terrible mission. The core gameplay is VASTLY SUPERIOR in GTA V. Everything from movement to weapon handling is just on a completley different level than San Andreas. The terrible aiming mechanic almost makes San Andreas unplayable in comparison to GTA V.
I really like San Andreas, and even thought it did things better than GTA IV, but at this point I think it's time to realize that it has been comprehensively surpassed.