Garen kinda shits on people who have no escapes and can't out trade him. If two juggernauts come into lane and one is Garen, then Garen will thrive if he gets an early lead.
He's pretty easy to play around early though. You can mess up his Q pathing pretty easily and if you respect the damage of his E then you'll know to avoid it whenever.
The only thing that you can't really avoid is his ult. True damage or no, it is going to kill you when you get low enough. The trick is to not get that low when dueling Garen (unless his ult is on cooldown or you're Olaf).
His silence is a bitch if you play ability reliant champions. But most auto attack based ones won't be worried.