It's not Garen, It's the Items So Stop Crying ( Down votes are coming :)
I used to main Garen pre-rework.
The point of his rework was to re-enforce his role as a carry tank mid-late game and allow him to finally stick to a target and be rewarded for it.
- He no longer has built in tenacity, 2.He has a reduced silence
- Lower Damage in laning phase. The only thing that really changed for the better was his damage with his E mid - late game and the Villain mechanic which is only actually useful after laning phase usually.
The actual reason he is currently so powerful is simply because he synergizes extremely well with the Juggernaut items maybe actually the best out of all the Juggernauts.
- Damage, Health and %Health Shield are the bread and butter of Garen's kit.
- Armour Pen, Health and Damage
- Movement Speed, Health, Armour and a Built in Slow to top it off what more could Garen want.
- Toooonnnsss of Health and a built in mini Garen passive
- Actually not that good because Garen has his E for wave clear and unlike the 
it can't be activated mid spin. So don't suggest picking it up.
As you can see these items give him all he needs, armour pen, damage, lots of health, and movement speed. I tried playing Garen without building any of the new items and he is basically just a watered down version of his old self. Then I tried with the new items and he was doing his job perfectly, getting to targets, soaking up damage and dealing a good amount of damage if they stayed in his E. So it's not that he's broken/op it's simply that the new items make him do his job extremely well. I do not personally think he is broken, because overall Olaf with the new items is actually broken.
