He held his own in the first half of the fight, mostly because Mayweather wasn't attacking much, and let McGregor wear himself down. In the second half, Floyd raised his game in each subsequent round, and McGregor couldn't keep up anymore.
The fight could've gone another round - maybe - but the outcome wasn't in doubt at all. The only thing the early stoppage did was prevent us from seeing McGregor get knocked senseless (as much as many were hoping to see it).
I think McGregor could be a boxing champ if he decided to leave MMA and focus solely on boxing. He has the physical ability, and the mental determination. All he really needs is to hone his skills with some progressively tougher matches. But considering he jumped into the ring with one of the best fighters in history, and held his own, I give him credit.