As a mid, I disdain any change that makes it easier for any other non-mid to kill me 1v1.
For whatever reasons, I haven't noticed as drastic changes on other AP carries, but most didn't have the huge pick/ban/win increase that Ahri did virtually overnight. But let's go over the pros and cons.
Orb of Deception
+ Gives a stupid-high movement speed scaling bonus on cast (which is what should have been nerfed in the opinion of many)
- Cost substantially more mana, despite being Ahri's primary source of champion damage and creep farming
Fox Fire
+ Revolves around Ahri 30% faster (which is completely irrelevant 80% of the time so how is this a pro?)
- Debuffed damage, shorter range
Charm
+ Nothing of note
- No more spell damage bonus, no major mana reduction since the first time cost was increased in S4 (as if taking DFG wasn't enough)
Spirit Rush
+ Nothing of note
- Rush dash range shortened by 100
Early game, rather than having the option of buying items like Chalice or Idol as with Season 4, it's almost mandatory now. Q is no longer as viable an option for wave clearing and farming, since it will be draining mana much faster. 1v1's leave her much more vulnerable to ganks now, since she's probably only remain with enough mana for either Charm or Orb, but not both. In team fights, she has to be more more exclusive about choosing targets to commit to; she can still get multikills, but they are usually from Rush or on already-low targets rather than melting anyone with a DFG cast.
There is a pro to this, but it feels incredibly cheated since it was always in the game to begin with; items such as Will of the Ancients give Ahri good health sustain, and Spell Vamp is a new core meta on her. It brings nothing new to the table though, and feels like a way to skirt around her other sustain issues.
YES, Ahri is a mage assassin, and always meant to pick targets and engages selectively, but with newfound emphasis on assassin which is ironic without DFG to commit to one target with as well as the de-emphasis on Charm (which was what her first ever rebalance specifically listed as Riot wanting to emphasize for her combo and now just feels like an accessory in Season 5), and she is still outclassed by people who are actually good with champs like Akali and Katarina, who will just ignore her, roam and take kills from other lanes and their team to get their feed. This means Ahri now has a higher skill-requirement than her original self, which is almost the opposite of the effect they wanted to have, which was making it easier for people who neglected or weren't good with Active items to pick up and use.
So basically, Riot contradicted what they wanted to see in Ahri twice. She isn't easier to use without the actives and her charm hit isn't mandatory for her combo anymore. All she has is that stupid mobility buff - she is outsustained and outdamaged now as a mathematical fact.
Rant over.