Garen is now one of the weakest bruisers in the game. He's outclassed by other bruisers like Renekton who does everything Garen does(Armor shred, CC, Self-Sustain, Damage and Tankiness) but better, Darius who's laning phase, teamfight presence, passive and ult is miles better and of course others like Camille and Irelia.
"Why do you think Garen is bad?"
Passive - Its worse Ocean Drake buff. Ocean Drake Restores 4% missing health and mana every 5 seconds while Garen's passive regenerates for 0.2 / 0.8% (based on level) maximum health every half-second and is doubled to 0.4 / 1.6% (based on level) maximum health every half-second while below 25 / 50% (based on level) of his maximum health. Its COMPLETELY outclassed by Ocean Drake and just to add insult to injury Ocean Buff is considered to be the worst Drake buff.
Q & Ult Cast time - Self explanatory, its too long especially the Q animation.
Villain Passive - Oh god. You haven't felt rage in League until villain mark moved from who you was fighting to another champion. It serves no purpose other than to absolutely ruin your day. Sure, Its nice to have against champions like Cho'Gath or Sion but thats about it. 8/10 times if you killed someone who has been marked as a villain you would easily do so without it.
W passive armor gain is capped - Why? Just what is the reason behind this? Why is Sion's W passive health gain not capped?
"Okay, smartass. What do you propose Riot to do with him?"
Passive - Not sure about this one, i'm thinking Armor & MR(or damage) based passive with little health regen.
Q - Make animation faster.
W - Uncap Passive Armor & MR passive and make it harder to farm them. (example = 55-60 Armor & MR at 200 farm)
R - Remove Villain Passive
E - To compensate for removal of Villain Passive buff the damage or alternatively ignore this buff and make R reset on kill.
This is it. I hope i didn't come off as too much of a Garen fanboy because i really am. I love this champion so much but it hurts to watch him being outclassed by almost every bruiser.