For me I loved 2 things about KOG.
AD machine gun.
and
AP Artillery.
Sadly Kog can't do any of these now.
They had Kog in a good place after his rework, why the decided to remove the AD Scaling in his W and completely obliterate his identity as an AD marksmen will forever be beyond me.
Seriously, he was in a good place. He was weak and immobile early game, but scaled amazing well into late game while still keeping that immobile weakness. Now that the AD Scaling on his W is gone Kog has no Reason to build AD and thus lacks any power then the other Marksmens have.
AP Kog also not so good, lower AP Rations and crazy high Mana scaling on R (Added with mana regen nerfs) make it virtually impossible to play AP Kog, especially in mid lane where AP Bursts and AD assassins easily obliterate him.
They could honestly fix all this if they just give him back the AD Scaling on W, until then Kog will continue to be where he is now, in a failed rework that made his identity crises even worse.