Oh, Roger's whole deal is so interesting because we never get a direct, blow-by-blow list of his powers like we do with current characters. The genius of Oda's writing is how he builds this legendary figure through implication and aftermath. From everything shown and said, Roger was an absolute monster in a fight, primarily through his mastery of Haki. He and Whitebeard were depicted as equals, clashing with Conqueror's Haki so strong it physically split the sky, a feat we've only seen replicated by the very top tiers like Kaido and Big Mom. He definitely had all three advanced forms—Observation, Armament, and Conqueror's—honed to a ridiculous degree. His main weapon was that iconic cutlass, 'Ace', so his swordsmanship was clearly top-notch, though it seemed integrated with his Haki rather than a distinct style. What truly set him apart, though, wasn't just brute force. He had this uncanny ability Oda calls 'the voice of all things.' He could 'hear' the Poneglyphs, understand Sea Kings, and intuitively navigate the world in a way no one else could. That's what let him reach Laugh Tale; it was a prerequisite no amount of pure combat power could substitute. His real 'power' was the charisma and will to gather a crew that could make that final voyage and to spark the entire Great Pirate Era with his dying words. The man conquered the Grand Line with a smile, which says more about his spirit than any technique ever could.
Watching the flashback in Wano, the sheer casual power on display is staggering. He parries Whitebeard's bisento with his sword like it's nothing, and their clash is portrayed as this joyous, earth-shattering contest between friends. It never feels grim or desperate. That's the key to understanding Gol D. Roger: his strength seemed effortless, a natural extension of his boundless freedom and curiosity. He didn't have a Devil Fruit, as far as we know, which makes his achievements even more insane in the current era of mythical zoans and logias. He represents a purer ideal of power, rooted in willpower, inherited will, and understanding the world itself. In a way, Luffy's path mirrors this—incredible Haki, a mysterious connection to the world's voice, and a crew that follows his dream—rather than mirroring the more mechanically complex powers of other Emperors.