Mega Man 9's story and gameplay are the same as they've always been - Dr. Wily is running amuck and Mega Man has to stop him. This time Wily's convinced the populace he's the good guy and it's Dr. Light who's unleashed eight robot masters on the city (total lie, of course). There are even "Dr. L" doors in front of the bosses instead "Dr. W."
As before, you have to defeat each robot master, steal their unique weapons and use them on the remaining bosses. Each is weak and resistant to specific weapons, so you'll have to experiment to see which plan of attack works best. And by experiment, GamesRadar means "die a thousand deaths," as Mega Man 9 is easily on par or above the hardest games in the series. Hell, they played for two hours and only made it to three bosses, and even then only beat two. Not too surprising considering they don't yet know which boss is weak against the other, but damn, these guys are hard.