Can't believe some Zoro fans have audacity to say Luffy has asspull powerups, when Zoro got breath of all things and Ashura out of nowhere. Even Sanji's diable jiambe came out of nowhere.
Meanwhile Luffy's powerups have been consistent throughout the story, have naturally progressed and explained in the manga. Gear 2 being like Doping, gear 3 is him blowing air into his bones, gear 4 is combining haki with gear 2 and gear 3.