I've made a list of some of the things you can do in San Andreas for any doubters or haters out there.

Home Invasion missions

Trucking missions

Hunter Quarry missions (don't know exactly what these are, haven't made it that far yet)

Car modifications

Customize CJ to your liking (working out, buying clothes, haircuts, and tattoos)

Fly passenger airplanes

Spray paint 100 tage across Los Santos

Go parachuting

Wage gang wars

Swimming (finally)

Take photografs, find oysters and horseshoes (sounds dumb but unlocks something really cool when you find them all)

Dozens of hidden vehicles and airplanes

More than 35 houses to buy across state and many business to buy