I know that that's the point of his character, but what I'm trying to say is that to me, the revenge he's after is not a compelling enough reason for him to be doing what he's doing. He was a criminal attempting to steal a bunch of money, and because he was involved with crime rings and shady characters, his niece end up dead. In my opinion, Aiden brought this tragedy on himself, and instead of realizing this he just gets more and more invested with the criminal underworld and puts his sister and his nephew in more danger than if he'd just done nothing. There are plenty of revenge stories that have successfully had me rooting for the protagonist, no matter how dirty their hands get. However, this game just doesn't get me to root for Aiden because I feel like he brought this onto himself, making all the deaths of others a result of his desire to blame others for what happened. He's like Kratos to me in this sense, where I just can feel for him because his whole motive involves killing others to get "revenge" for something he is responsible for.
I don't have a problem with flawed characters or morally grey ones. My problem is that the game doesn't seem to be self aware enough to ever address the fact that Aiden is doing more harm than good on his revenge quest. The game seems to expect the player to just be along for the ride and agree to do whatever it takes to avenge his niece. Like I said in a previous post, I didn't mind playing as deranged sociopaths in GTA V because the game didn't try to pretend they were anything else, whereas it seems to me that Watch_Dogs doesn't want to player to realize how big of a hypocrite Aiden is.
Of course, this is just my opinion, and I haven't even finished the game so maybe I should wait for Aiden's character arc to complete. This is just something that's really stuck out to me about the plot.