I think Rockstar did it right with GTAIV. The Lost and the Damned and The Ballad of Gay Tony were excellent DLC. They created one world then created multiple stories in that world.
I liked EFLC as well, but just imagine if they had pulled a San Andres on it like they did with GTA3. EFLC wasn't 2 full games in one. It was two DLCs sold together that were far far shorter then the original game. In contrast Vice City and San Andreas were much bigger and better than even the original. Imagine what they could have been if they were stand alone games.