Well, most of these characters are the ones I use (Raiden and Nathan are my main mains). This is my opinion and I have talked about this with my friends and they agree too. Here it goes:
Raiden- he needs the unlimited grab fixed (nerf to 2 max consecutive throws, if that is possible), reduce AP gain by a little bit and to make people happy: reduce range of Level 1. IMO Raiden is not that OP.
Kratos- reduce AP gain significantly, pretty much thats it.
Cole- that hero gains AP so fast, especially to his Level 3 (his Level 3 should cost more).
Evil Cole- his cirlce (charged) attack goes very far, need to lessen its range a little bit, his bolts need more AP gain: they are slow compared to Cole's and yet he gains less.
Big Daddy- super fast to aquire Level 3.
Heihachi- "that bear!!!" slightly reduce AP gain.
Sly Cooper- Sly gains AP very fast in the game and with his level 3 he can kill up to 7 (7!!!), I think his Invisibility should cost 1 AP per second, gain less AP for all of his attacks, his Level 3 range should be fixed to more closed: they should "hit" the character to kill it (they can kill me without even aiming at me).
Thats pretty much it, maybe I forgot something... as u read, I even mentioned some buffs for some characters.
As a Sly main, I wouldn't mind if they made his invisibility drain a little AP. I think that's a decent way to keep people from abusing it. Currently, the only reason would be that it makes it a little harder to see yourself, but people still seem to abuse it (apparently - I haven't seen people do that myself).
I will have to disagree with you on his level 3. Anyone who can air dodge and roll can avoid it pretty easily. I also don't understand how you think he gains AP the fastest in the game. Perhaps it was an exaggeration, but it was not accurate at all.
I dodge it, sometimes... If you aim lowest way possible, you can kill enemies without the center reticle aiming at the enemies.
Sorry, maybe not the fastest, but still, he gains AP very fast, maybe due to his AP stealing or something. Again IMO. Thanks for commenting.
Kratos needs the range and tracking on his chain grab lessened, his AP gain nerfed, and either his attacks made slower (like in the actual GoW games) or given some sort of cooldown.
Evil Cole needs no armour on his Gigapunch, and being hit while charging it should reset it completely.
Sly isn't terrible, he just needs his level 1 to be more interruptable.
Evil Cole's attack is fine, other than that they all look fairly reasonable. Although, I do think that that Radec's sniper rifle needs some nerfing. There are too many players just using that over and over again, they should just reduce the range or take away the launch effect it has.
Sniper spam is literally the last thing I think they need to change. It's also the hands-down easiest spam to dodge.
It's an annoying combo breaker.. When you're in the middle of a combo, some cheapo from the other side of the level just uses this move over and over again, and they gain more and more AP from the weaker players. And then they get to use one of the most effective level 3.
Also, I don't agree with the cost for Sly's invisibility. He has no dodge, unless you consider his counter move the dodge. I think it would take away one of the basic defences that Sly has.