In Patch 4.17, Riot hit the right champions with the wrong changes.
This patch, Riot seemed to do a great job hitting champions who actually needed buffs and nerfs. The problem is, with the champions they buffed, they added power that's unlikely to make any significant difference to their viability. The champions that got nerfed either didn't lose very much at all or got absolutely crippled, with nothing really in between.
I'm not going to talk about the Viktor or Soraka reworks too much here because they're brand new and people need experience playing them before we can pass judgement; I think the Viktor rework looks like a (nearly) straight buff while Soraka's is too different to make a prediction.
#Wrong Buffs at the Right Time

Garen's definitely needed buffs for a long time, so it was nice to see him getting some for once. However, instead of hitting the area where he most needed help (his ridiculously long cooldowns, especially in the laning phase when his ultimate's cooldown is 160 SECONDS at level 6, longer then the ultimate cooldowns of fellow top laners Riven and Darius as well as that of Jinx's ult. Jinx's ult is especially notable in this case because it deals 50 (+3.75% opponent's missing health) less damage, but has an AD ratio, global range, and can be used nearly twice as often.
Instead, Garen got a lategame buff to his passive, which would be alright if people picked Garen for late game. Nobody picks Garen to scale late game; they pick him to win lane early and have a good contribution to mid game teamfights. Thanks for buffing him, but better late game power on his passive is not what he needed and will not improve his pick rate. Literally all he needs is for his ultimate to have a similar cooldown to comparable abilities that are already BETTER abilities even before considering the cooldown.

After her rework, Cassieopeia has largely fallen out of favor due to the massive loss of lane phase power she took in exchange for slight buffs to her already strong late game. With any rework, power tuning is hard to gauge on PBE, so the buffs coming in for her are good. The problem is, while the E bugfix was sorely needed, buffing the AP ratio on her Q (another late game buff) is not going to help much at all. Post-rework Cass only uses Q as a poison-marking tool, since E's mana restore+health restore mechanic means it's never worth it to max Q as a lane harass tool.
Sure, raising the AP ratio on Q helps her damage late game. But even pre-rework, Cass didn't have any problems wrecking people's shit late game. What she needs to be viable in the assassin metagame is some of her old lane prescence back. Maxing E first, all of your damage potential in lane is coming from Q/W->EEEEE, which is very short ranged and leaves you completely vulnerable to hard engage by enemy assassins. Cassieopeia's early harass pre-rework was the only way she could not get wrecked by mobile assassins. She should have gotten base damage buffs on Q or gotten Q's old cooldown back, not an AP ratio buff.
#Right Targets, Wrong Nerfs

As a Trist player, she's definitely really strong right now. I'd argue that more of her power comes from the itemization changes then from her kit, because she only gained popularity with the 4.10 itemization changes even though her kit has been largely unchanged for years. I don't mind an experimental nerf to see how it hits her, but the nerf you took was entirely the wrong one. Tristana's ultimate was not the source of her lane power, nor is the cooldown really that important to her power (it's rare to have full all-in trades with everyone's ultimates blown more often then 100 seconds in lane). Increasing her ultimate's cooldown barely affects her power, and she'll still be played just as often because all it does is make it so she can engage an all-in on her terms slightly less often.
Instead of nerfing her ultimate's cooldown, you should have considered hitting ADC itemization; that is the real root of Tristana's current balance issues. If you absolutely had to hit Tristana before addressing itemization again, then you should have changed her Rocket Jump's cooldown reset on kill to 20/40/60/80/100% reset. This would force her to max W in lane to get the full reset before mid game starts, forcing her to choose between early poke and the ability to escape after her all-ins in lane. Now she has to choose between maxing E first (which gives her poke but autoshoves the lane and makes her towerdiving entail heavy risk) or maxing W first (which limits her effective trading to all-ins, allowing AD casters like Lucian or Graves to bully her out).

Contrary to popular belief, Talon really was strong for a very long time. Riot's logic for removing his silence was good, but he needed some kind of compensation for it and got nothing. Let's face it, a 99% slow that only lasts for 0.25 seconds is a joke. ANY CC that lasts for 0.25 seconds is a joke. Talon was the only remaining assassin with a silence, and that gave him an important niche in lane compared to much safer assassin picks like Zed and Yasuo. Now that he's lost the silence and gained virtually nothing in return, I just don't think he's different enough from Zed or Yasuo to be worth picking over them.
Note that I'm not saying that this nerf was unjustified. Getting 100-0ed while you're silenced the entire time is bullshit (which is why LeBlanc and Kassadin lost their silences). I'm saying that this nerf hit the only reason to pick Talon instead of Zed, and should have come with serious compensation with that in mind. Instead, Talon lost a significant amount of power and got nothing in return.
#Final Words
These kinds of changes are bad for the game in the long term. Hitting overpowered champions with nerfs that don't reduce their power is stupid, because you're just going to end up nerfing them again next patch. When you eventually hit the right note, that champion is going to be absolutely crippled because you took away every tiny bit of power they had BEFORE actually hitting the reasons they were popular, leaving them with a shell of a kit bound for a rework. The reverse is true for buffing underpowered champions with things that don't actually help them at all in their current state; when Garen finally gets the buffs he needs (damage on Judgement + cooldown reduction on his ult), he'll be overpowered thanks to the all the buffs you give him while trying to ignore his actual problems.
Removing toxic mechanics from a balanced champion is fine, but you have to give them compensation. It always seems like all the wrong champions are getting compensation buffs, and this patch is no exception; Nidalee got a buff to her Q's AP ratio and a buff to her cougar form W in exchange for losing AD ratio on her Q, while Talon lost A CROWD CONTROL and got absolutely nothing in return.
We're all glad that you're trying to improve League's balance. You just missed the mark on this patch.
and in a teamfight she would have an additonal 40% for a grand total of 75% and be rid of the slow im .07 thats not enough time to give
most op champion" hype that was boiling around in summer