As if by magic...
I think it's a reasonable likeness, but I'm of the opinion that a portrait should look more like the person than the person does, which requires some slight exaggeration, but what you've done is nudge the features towards an average face, which makes it look less like him than he does.
I've gone into more depth on the subject just a few days ago in this thread - http://community.imaginefx.com/forums/thread/356880.aspx
This kind of also brings me to something I've been meaning to say to you. Recently you've been making some big improvements in your art, but I think you seriously need to think about faces more. It seems to me that you've gotten into a routine, when drawing characters from your imagination, of using stock features, and the result is a samey-ness in your characters' faces (male or female) - the same kind of eye, nose, mouth, and jaw shapes crop up again and again, in heads which have practically identical proportions. Other than hairstyles, they are all pretty much interchangeable.
I'd like to see you try and get some more variety into your faces, and this thread is the perfect place to try it. One technique is to "cast" an actor, or a combination of two or three, in the role, and distill the essence of their features into your style. It doesn't have to be a likeness (that can actually be distracting in a comic) but their "type". And don't be afraid to push the differences.
To give some examples from real comics: Gil Kane based Hal Jordan (Green Lantern) on Paul Newman; Brian Bolland based Psi Judge Anderson on Debbie Harry; Gene Colan based his Dracula on Jack Palance. None of these look exactly like the inspiration, but they are of an ilk.
So, who would be the ideal choice to play Mercy?