Bingowings said:

Not bad, he looks enough like him to get the idea across and he is a fun actor who could have given the role the necessary coldness.

Nobody seems to care that Ewan doesn't look or even sound exactly like a younger Sir Alec.

If they were serious about putting Tarkin in the prequels they should of written a role for him and hired someone like Nighy who could have played him without OTT make-up.

I don't think I agree with that part. They did a decent casting job there, he does have a lot of the same features as Alec Guiness did. As for sounding like him, I think McGregor really did try his best to be like Guiness in voice and "style" (actually, maybe a bit too much, I think it's reason his acting in the PT is stilted at times, especially in TPM, he was concentrating too much on being like Guiness).