I used to think that Garen's W is completely trashed, but I did the maths and...
By farming, you're getting a bonus of Armor and Magic Resist that normally would have made you buy 150 Armor and Magic Resist to get that bonus from the old W passive.
Plus, with the new 10% Bonus Armor and Magic Resist mastery, you can get half of your old W passive PLUS the bonus you get from farming creeps and killing champions.
That is actually huge.
Basically, you can get one Armor and MR item, then proceed to buy Damage and Health with the new items, and you'll still be as tanky as before whilt dealing twice as much damage.
Garen was significantly buffed this patch.
Like here's an example of what Garen's build will be this patch:
Titanic Hydra Sterak's Cage 
Tons of Resistances, Health, AD and movement speed. Plus, you have the tenacity and slow resistance, so you're still very good against CC.
You can replace the for a 
or
if you don't plan on splitpushing.
for more ms and slowresistance, or
to get more tanky vs AAs.