Sorry; this is straight-up copied from GD (it's my own post, but still). As such, it's not in my usual bulleted-list, well-ordered-sections format. It's also censored.
I'd say that it's not worth the read if you're not already familiar with Top in general.

The nerfs mentioned for Riven's kit:

  • Broken Wings (Q): Damage changed from 30/55/80/105/130 (+70% Bonus AD) to 10/30/50/70/90 (+40/45/50/55/60% total AD).
  • Valor (E): Shield duration reduced from 2.5 seconds to 1.5 seconds.

Some of the nerfs mentioned for meta toplane items:

  • Sunfire Cape: Magic damage per second changed from 40 at all levels to 25 + champion level.
  • Spirit Visage: CDR reduced to 10%.

RE: PBE Riven Nerfs

Building straight damage was only ever viable if you were ahead (her kit was good at getting ahead, but junglers are a thing); Chain Vest is ****ing strong, and it's the standard for the Toplane Super Bruiser meta right now. Everything you fight will pick up a Chain Vest on their first back and if you're even, those two Longswords you're going to buy for the same amount aren't going give you an advantage. 20 AD doesn't beat 40 armor ever. You lose until you buy more things. Crunch the numbers if you want.

Previously, Riven won lane early. That was it -- you either got denied CS or you got killed or your jungler camped your sh*t so you wouldn't have your anus handed to you. Those who have done the math have demonstrated that Riven's very early game is weaker (unless she has 0 bonus AD?). She deals less damage at level 1, so that level 1-all-in isn't as strong. Her level-2 all-in isn't as strong. Her level-3 and up trades got massacred with the shield change.

That extra second of vulnerability means that every top laner that extended trades longer than 1.5 seconds (read: almost all of them) now deal more damage to Riven -- and she deals less damage to them in exchange. Building pure AD was viable when ahead, and Riven was expected to be ahead in most lanes because of her trading strength. I don't expect that to continue to be the case.

As such, building straight AD on Riven isn't as viable, period. Furthermore, even if she does viably build straight AD because she managed to get ahead with her marginally-weaker trades, it won't be as effective. Lower ratios mean decreased return from items (this is not debatable), but, on top of that, the AD bonus on her shield won't matter because it won't last for an entire trade, anyway. Make the shield as big as you want: it will never get popped in lane unless you're getting ganked, losing horribly, or... what, taking Shock Blasts to the face? Elise bursts, maybe? The shield no longer has a meaningful AD ratio in lane, so those two Longswords you build with your Chain Vest money are going to mean even less. That now-hard earned gold gleams a bit less in your hands.

Someone mentioned that, hey, Riven can build a Chain Vest, and, yes, this will keep her strength relative to that of her lane opponent (if they are dealing primarily physical damage, but is that even a thing anymore?). I have rushed Sunfire on Riven and won lane for it: Immovable Object Riven was viable and scary. It wasn't as good a build for roaming and getting fed out of your mind, but it made you a complete monster, domineering in the hardest way in lane when you were ahead. Now that so much of that roaming gold is going to waste, though, maybe being an Immovable Object Top is a more-viable playstyle?

Except Immovable Object Toplane got nerfed across the board, and moreso for Riven in particular. The across-the-board nerfs to Sunfire and Spirit Visage (i.e. "every toplaner") mean that champions building those items will deal less damage (Sunfire) and apply less utility (Visage) across the map. 10 damage per second on Sunfire can be the difference between killing something and not; 10% CDR is easily the difference between having that stun up once or twice in a gank (on top of impacting how fast you get there, to begin with). Since the items are weaker for all of Top Lane, this doesn't really affect her laning strength outside of making damage more viable (which might be a buff, if not next to the hit Riven took to the efficiency of gold, in general), but it does affect every toplaner, including her, in their ability to apply themselves in other areas of the map. Hourglass and Blade of the Ruined King and Spirit of the Elder Golem are the same; only Top was really watered-down.

But the impact of the nerf doesn't stop, there. Okay, the nerfs to defensive items make offense more-attractive. That's cool. But there's yet another downside to building damage that I think a lot of people failed to consider, and it's honestly the one that bothers me most: building damage means maxing Q first in order to maximize your gold efficiency. No, it will never be as good as before, but the difference between a 40% and 60% ratio (or a 120% and 180% ratio over 3 strikes) is still huge and worthwhile. If you're building damage, you're now wasting gold unless you're maxing Q. Accordingly, maxing W and E is now less viable.

Maxing W and E was a fantastic option. Increasing your utility increased your map presence more than maxing your Q because those abilities were so much better for skirmishing. Like that 10% CDR lost on Visage, a few seconds off of the cooldown of W and E was often the difference between catching a target and not, and that mattered more in roaming because landing a stun meant that your teammate could apply their damage, and having your stun and shield up a few seconds earlier made you a much bigger threat in a 2v2 or 3v3 than having 300 extra damage on Q. You, your mid, and your jungler could easily contribute more than 300 damage (or they were doing something very, wrong) via your AoE CC and increased chasing potential, so the extra CC, defense, and mobility was worth the damage you lost.

But you don't lose 300 damage for 4 points in Q, now. You lose 240 (+0.6 AD). If you had more than 100 bonus AD (read: one finished item), this latest series of nerfs has actively harmed you for being a team player: if you want your own gold to matter, you max Q, and you let your team CC for themselves. Maybe they shouldn't need ganks; serves 'em right, eh?

On top of maxing W and E as an effort to be a team player, what about W/E Riven's impact in lane? If you were winning lane already, you didn't need more damage. More, faster CC and mobility was so much more attractive not only for your ability to roam, but also in winning your own lane harder. Added chase potential increased your threat zone, flat-out. Being able to hit E twice before your opponent reached turret was a f*cking ordeal for them, and that would often snowball a lane harder than more damage because, at a certain point, they couldn't fight you, anyway: the ability to make them fight you was more valuable than winning those fights by an even-bigger margin. It doesn't matter if you killed them in half of a rotation or a full one; they're going to die. It matters so much more whether you can drop zero or one rotations on them, and W/E answered that question. Answered. You don't get to do that, anymore; you fall off if you're not maxing Q, cut and dry. The possibility of early utility is no longer a consideration. Moreso because of the E nerf: as before it doesn't matter how big the shield is if it's never going to pop.

TL;DR: the nerf doesn't just "make Riven less snowbally with items". It locks her into a single viable skill order. It makes her a smaller asset to her team in general by hurting her roam and skirmish in several ways. It makes her snowballing not only less-effective, but less-likely. The systematic nerf of toplane bruiser items makes less-valid the alternative options to glass cannon. This nerf and its accompanying changes not only decrease the Riven's current strengths, but also flatten her as a champion by removing alternative playstyles: you've not only gutted just one of her playstyles, but you've also effectively locked her into that one.

I'm yet to applaud the balancing act that actively reduces the variety in the game, and I'm yet to see the red post that applauds it.

"Patch Notes: 4.1: Removed all Champions except Poppy" would instantly make the champion pool 100% balanced, but I'm sure there's a reason why that's not been the balancing act of choice.