I definitely think so. He's so much more likable, and this film is so heads and shoulders better than Chinatown. Both are atmospheric in a way that puts other filmmakers (Terence Malick, for one) to shame.
The opening sequence where the ghost gets beat up reminds me of the nose-slitting scene in Chinatown. Neither hero caves. What I don't understand, though, is why--since the Ghost himself says out loud on the phone at Heathrow that Kroll (Timothy Hutton) might purposely have set him up with the fake manuscript--Polanski never explains Kroll's reasons or whether he is also CIA, or just in Ruth Lang's posse.
Oh, the mugger can definitely just be one of those Hitchcock-like thugs who act as, you know, Mr. Gatekeeper to...Trouble . The Ghost hasn't left London yet, kind of like Roger Thornhill hasn't left New York after escaping from his own Gatekeepers to...Trouble. Unlike Thornhill (and Jake Gittes), he has a healthy Everyman amount of cowardice and lack of curiosity. He calls his agent to report the mugging, who laughs it off, calls the agent *again* from Heathrow, who laughs it off again--so basically the mugger just acts as a device to show that The Ghost is a 'Fraidy Cat not interested in being a cocky hero.
My only complaint with Ewan MacGregor in this role is that he doesn't sufficiently show his fear, which the script insists on again and again (when he first arrives at that stunning sterile house), when Dep and Mr. Dep give him the stink-eye, when he goes to that incredibly atmospheric deserted hotel (the DVD commentary states that the hotel was a real one that was really deserted).
But MacGregor really conveys The Ghost's dedication to his profession, so mocked by the publishing executives (and Ruth), and then his dedication to unraveling the mystery of his drowned colleague. You couldn't find two actors more different at the ages they made "Chinatown" and "The Ghost Writer" than Jack Nicholson and MacGregor, but when you think of it, Jake Gittes remains as monotonous as The Ghost. The Ghost doesn't need a damsel in distress in order to motivate him. He just needs Eli Wallach.
Dep and "Mr. Dep" are the (take your pick) frightened or frightening Pacific rim servants. The Ghost most definitely is frightened by them, even though all Dep does is make sandwiches and health-drinks.
The motorcycle thugs are either (take your pick) CIA thugs following idiot Kroll, or CIA Kroll's hired hands. The movie never makes this clear, but maybe the novel does.