The fact that R* somehow managed to triple the size and content over Vice City in the same console gen was nothing short of phenomenal (I'm not a techie but I seem to recall that they pioneered some form of dual-layered writing on the disc to cram it all in). I can't off the top of my head think of a same-gen leap from one series entry to the next that even comes close to it, and the fact that it crammed this all in without feeling bloated or unnecessary was a major feather in their cap (there's probably some who were argue certain side content felt like wasted space, but on the whole I don't see this as a controversial take).
That's a good point. Closest I can think is maybe... Super Mario Bros. 1 to Super Mario Bros. 3? ---