McGregor's young Alec Guiness was one of the very few good things in the prequel trilogy. Now, Hayden Christianson... if there was a less convincing block of wood to play such a pivotal role to be found, I'd be impressed.
I'm thinking in terms of big summer blockbuster movies here (despite recently seeing Dustin Hoffman being AWFUL in Perfume).. so how about
1) Kevin Costner as Robin Hood (Prince of Thieves)
2) Keanu Reeves as Jonathan Harker (Dracula)
3) George Clooney as Bruce Wayne (Batman and & Robin)
Yeah Hayden Christensen is one of the ultimate shitty pieces of casting. He was better in Revenge of the Sith but only marginally. As if anyone can believe THAT guy became Darth Vader. I think George Lucas was more interesting in getting someone closer to an older Jake Lloyd (who played Anakin in episode 1) but he didn't have to make him a crap actor as well!
Ewan McGregor's fairly dodgy performance is like Brando in comparison.
So many to choose from but I would have to say Keanu Reeves in anything. I have seen trees in films with more charisma.
Kevin Costner in Robin Hood Prince of Thieves.
Benjamin Bratt in anything. He is like Keanu Reeves's younger brother.
Richard Gere in Pretty Woman. Love the film but he is just creepy.
Renee Zellweger in Bridget Jones (especially the second one).
Andie McDowell in anything. She can't act for toffee and when that advert comes on, I want to throw my tv out of the window. You are old and haggard - no product will help you!
Jude Law in Alfie (why even bother to re make this film - there is no one like Micheal Caine..)
Jim Carrey in anything..and ditto Robin Williams
(can I go on....three just isn't enough!)
Brad Pitt in Troy (in fact everyone in Tro!)
Daryl Hannah in everything except Splash
Cameron Diaz except when she's playing ditzy cute blonde
Drew Barrymore in any role when she is the babe (?)
Jack Nicolson as the Joker in Batman, right temprement wrong body shape.
Micheal Keatin in the same film, right Bruce wayne wrong Batman.
Tom Cruise in any film.
Sam Neill. I thought of him to play Robert Langdon as soon as I heard a film was being made of the book. And John Malkovich as Silas the Monk, rather than Paul Bettany.