TBOGT was sort of a bone for people who wanted more over the top San Andreas style gameplay and it worked great. It had a more lighthearted story and over the top weapons plus fast and flashier cars and an attack chopper. It also had over the top missions.
Some people complain that V is too over the top and shallow so why not throw a bone to people who want IV style gameplay and story. Make a dark and gritty story and make the driving and handling as IV like as possible the way TBOGT sort of tightened up the handling.