As Dark Raven said, classic Rocket was never part of the original GOTG; but yeah, there's a huge difference between the Rocket that existed before 2008 GOTG and Rocket as DnA portrayed him. Classic Rocket was little more than a whimsical character that existed out on the fringes of Marvel fandom. He was basically part of a quaint little fable about anthropomorphic critters who were basically pets/guardians of an intergalactic lunatic asylum. The whole miniseries was written and drawn in the style of a nonsensical Beatles cartoon like "Yellow Submarine" (and even featured quite a few references to Beatles tunes).
But when DnA got through with him, he was an ass-kicking rodent (marsupial? whatevs) with oversized big honkin' guns.