I'm going to go through the patch notes for the release of Sejuani and give my thoughts on the changes.
The PvP.net changes are meh.
Sejuani, The Winter's Wrath
I'm excited about her. It seems like Riot is finally understanding how to build and design tanks. Also, her frost triggers Anivia's Frostbite - very nice.
Ahri
Nerfed
This isn't crippling for her, but it hits her early game harass and her late game escapability. This shouldn't be that bad for her. A small nerf.
Dr. Mundo
Buffed
This is huge for Mundo. His base stats got significant buffs, and his survivability got buffed via a CDR decrease on his ultimate and less Health per second on his Burning Agony. He might actually be good now. This is exciting news.
Fizz
Bugfixes
Graves
Nerfed
Wow, did they really have to hit him again? And this time, it might be for good. This is a significant nerf, especially on top of the previous significant nerf.
Jarvan IV
Buffed
He's back! Very fun to play, but extraordinary mana issues early-mid game have relegated him to low-tier status, and certainly lower than almost every other tank. This fixes all that! Or, at least it just helps out a lot. Very exciting news.
Jax
Remade
This looks like a potentially very strong remake. Jax could be very scary, or he could just be even easier to play around now...
Nunu
Buffed
Slight buffs, but really not that much. This will help him Jungle, certainly, and make him a tad more viable late game.
Rammus
Nerfed
They nerfed his ridiculous mobility a little bit - this is mostly important for Dominion. They also slightly nerfed his only real source of damage, which is a bit strange and probably unnecessary.
Riven
Nerfed
They really hit her sustainability with this patch. Also, they made Ki Burst less the "obvious choice"
Shaco
Nerfed
They hit Shaco's Jungle here. They also hit AP Shaco pretty hard due to the max 1 minute duration of a nest of Jack-In-The-Boxes. But that's ok because AP Shaco is terrible.
Skarner
Nerfed
Well, he's now been nerfed straight back to hell. It's a shame that they can't seem to find a middle ground. When he was released, he was underpowered and had huge mana issues. They fixed that, but overbuffed him. No one seemed to notice for quite awhile, and then suddenly people realized how ludicrously powerful he is. Now he's been completely overnerfed. This is kind of really disappointing.
Tryndamere
Nerfed
Hit his sustain, hit his early game dominance. These needed to happen pretty badly.
Vayne
Nerfed
How many nerfs can she take before she is finally unviable? I think this won't stop people who really want to play her, but it's strange that they hit her and not Caitlyn. Now Caitlyn is pretty much obviously the dominant AD Carry.
Volibear
Buff/Nerf
In general, they just moved his damage capability around. He no longer only deals damage with Frenzy. Well, he still kinda does I guess, but he has less burst and more sustained damage potential.
Warwick
Buffed
Slightly. This feels much better for him.
Xerath
Bugfix
Items
Ionic Spark replaces Sword of the Divine. This is a good thing.
Ninja Tabi are... ok again. We'll have to see if they're still any good without stacking dodge.
Stinger and Nashor's Tooth buffs. Yay! Teemo!
Summoner Spells
Surge got buffed by a lot. Might be more useful now. It's on the same CD as Ignite, sounds good.