The changes in his metabolism include tremendous strength and invulnerability, along with super speed. He now resembles Superman, but without the flight. His skin also turns red permanently, forcing him to do away with the secret identity gig and officially joining the police force as the Flash.
His career would change much more than his powers did. Being a sanctioned officer of the law, he patrols the city constantly, making Central City almost crime-free. From dealing with street crime he learns early on that an unarmed opponent is almost no threat whatsoever, so when a shmo like Capt Boomerang or the Weather Wizard shows up, he removes their gimmicks before they ever become a real threat.
And of course there is that inevitable first meeting with Superman, which turns the Man of Steel into a six-foot talking banana. Too bad they were fighting Gorilla Grodd at the time! Ouch!