He has had straight nerfs since before 2012. Now his Ult, even though it hits, does lackluster damage to anyone who has a mind.
Gangplank needs a slight buff to his passive, e and ult to get back in the game.
He is overscaled by other champions. 
He needs a rework to be honest.
I play a lot of gp on my main and I honestly feel like the ult change was a nerf. It's more consistent now but in terms of overall damage, especially in jungle team fights, is less than it used to be. And those lucky ults where they get hit by a shitload of balls just felt amazing.
As a Gangplank main, I too feel that the ult changes were slight nerfs to our mighty pirate. However, it is at least a good sign that RiotGMang is still working on the rework and isn't going to abandon it halfway.
The recent change to his ult was a buff
The change in his ult was sort of a buff/stealth nerf. There has been many times that I used to ult someone who had escaped past their turret with a bar of life left. In the past this was a sure kill. Now it has to hit them twice to kill them and sometimes they get away. I would suggest that they take the total damage possible from the cannons and give 33% of the total damage on the first volley and then make the second volley less than the first, maybe 25% of the total, the third volley do 15% of the total, then have three volleys do 9% of the total each. This would help a lot. Think of the other global ult, Karthus's, he hit everyone on the map for most of the time at least 25-33% of their life in one hit. With GP's ult your are lucky to get more than one hit before the enemy walks out.
