Rocket was far stockier and bulkier in his original depiction, while Drax was a bit leaner (and meaner) and maintained the character’s more traditional tattoo look from the comics.
However, arguably the biggest changes were the ones made to Groot, as his original form had a far more skeletal and human (a.k.a terrifying) appearance.
Star-Lord and Gamora clearly had their costumes undergo some major shifts before production began, but that’s nothing compared to the other members of the team.
While the DNA of the Guardians of the Galaxy characters is still on full display in that early concept art from Comic-Con 2012, it’s clear that quite a bit of fine-tuning and refinement went on behind the scenes before Marvel landed on character designs that worked for the franchise.