Time to get nit-picky!!!
After looking over the picture, well, first I noticed it should be Red, not Read for RDR.
And as far as characters that defined gaming, I would say just one per franchise would be good too.
I like a good number of the picks, though I would just leave either the portals or GlaDOS and remove the other Portal stuff, keep only one of Layton or Wright, just Shepherd from Mass Effect, and only one GTA character (probably Vercetti). (And scrap Kaim). I think the guess of Loghain might actually be mistaken, unless you can get confirmation from the thread or painter, or whoever created the image. My guess is that could be a representation of the player's character in Dragon Age.
I would replace the removed characters with:
Dante, Devil May Cry
Player Character, Fable
Some random character from WoW
One of the playable characters in Guitar Hero
That's all I can think of for now. I might add more as I think of them.