Short 5.2 feedback
Ahri's going to need a mana cost reduction to fit in with having to throw out more spells to do the work - her E especially could probably stand to pull some mana out of it. She's been going oom rather quickly and as her kit is now built to kite rather than burst, it means that she'll have to do more work to get that damage out.
Tristana's scary as all hell early right now. Later in the game I've seen her both get thwomped and win hard, so I can't speak on that right now. However, she will need a bit of balancing throughout her game (not necessarily a nerf, but a power change to alter where she starts spiking).
Assassins are still generally doing fine. They're no longer tank busting, but mages do that well enough, so we're bringing an active choice to players between the two options, and that's good.
Removing grievous wounds from Fizz may have been a bit of an overshoot. While it had a tendency to seal the fates of people due to their inability to heal back up, it was also a mechanic that was unique to Fizz, Tristana, Varus, and Miss Fortune as champions. It put Fizz in a good spot to be a viable choice against Mundo and Vlad as it gave him the ability to actually not only assassinate squishies but also support through tactical play. Vlad is now a very hard counter to Fizz, and hard counters aren't exactly healthy to the game in any way.
Annie's new utility makes Tibbers more than just a one-stop-drop, which is nice. It was frustrating trying to get him to chase down enemies with how slow he moved.
Akali's now far less overbearing to mages, which for a good number is a good thing with the removal of DFG - now rather than sweating beads about how they'll be able to eat her before she eats them, they can just stay a good, safe distance away.
Rek'Sai's damage nerfs seem a little aggressive for her early jungling now considering one of the main selling points she had was a jungler that could thrive in clearing the new jungle, but people may find a middle ground.
Zed may need a bit more than that considering the safety he holds - Fizz's ability to all-in 1v1 people pre-6 has been pretty reliably mitigated, but Zed still holds the ability to poke to half and then AA-bumrush the target. Also, with the removal of DFG, a lot of assassins will likely have been put in a more reasonable place, where Zed was still thriving without the necessity of such damage steroid items - he's going to need an adjustment or he'll just come crashing into the top-pick list.
Speaking of which, Janna and Jarvan are going to need adjustments soon as they continue to not only bump out other champs in such roles due to their reliability but also continue to be very overbearing in one way or another (Janna is able to engage stupidly well on top of being able to disengage phenomenally, and Jarvan even building straight tank can still gib an ADC within a few seconds). I would suggest starting with Janna's very strong shield and the strength of her slow which basically ensures that anybody caught out is doomed, and for Jarvan I would take a look at the passive you buffed a while back - it hits very hard early. Maybe lessen the damage against champs earlier and give it a bit of a boost against monsters?