Yeah, I'm a little more in shock about his W changes. 20 + 70% armor/MR at rank 5?!?! Holy crap! If he has 300 armor from his base armor and runes/masteries/items, that gives him an additional 230 armor, instead of 120 like it used to be!
O.O
He's slowed by 60% during it now though, although it won't really matter since you weren't really activating when you planned to move around anyways. Plus it's cool down got more than halved.
Taunt + stacking slow from Tremors means I'm not worried about that little self-slow. Rank 3 ult stacks up to 96% slow... Yeah... They aren't going anywhere.
The damage of his W was changed to be his new Passive though I think, which is overall less until you get into the very big extremes of Armor (like 400 or so). His damage was overall nerfed, but he got more utility, durability, and mobility. I think this is nice.
If you build 7 Thornmails, you will end up with over 1200 Armor during his W and take less than 4% physical damage. Rammus gonna be big! Because that's a totally viable build...
Well, let's look at an actual full Armor build that I usually use as Rammus:

That's a grand total of 444.5 without Runes or Masteries at Level 18. So, if we used W during that, we would have 775.65 Armor for the duration of the W and reflect a grand total of 229.135 plus 15% of the damage dealt magic damage every time someone basic attacks us.
Hmmmm...
So let's say that I'm an ADC. With 250 AD, and 2.0 attack speed. Assuming half of my attacks crit, over a period of 5 seconds (10 attacks, 5 normal, 5 crit) I would deal 3750 damage before armor. 10 attacks means I take 2291 damage from your W, and Thornmail means I take another 562 damage, for a total of 2853 damage I am basically doing to myself, pre-MR.
Rammus, on the other hand, would take only 376 of the 3750 pre-mitigation damage...
Wow.
Except every ADC has at least 30 MR and you should probly buy a hexdrinker to counter the thornmail/rammus W/ general magic damage.
And you also have life steal.
With a MAW alone (not counting the runes) you have 44% magic damage reduction. Which would mean that 2200 damage gets reduced to around 1300 damage.
1300 damage isn't going to be hard to life steal through considering all his other damage has been nerfed.
Especially if you build giants slayer and maybe a black cleaner.
New rammus actually looks terrible. I consider it a nerf to every single ability.
But ap rammus ;-;