In another interview with Irish crime author Declan Burke, Child spoke to his fans' backlash at Cruise's casting.
I think the backlash is partly Child's own doing in identifying Reacher so often by his size. Perhaps if he didn't, we'd be able to imagine any number of actors playing Reacher.
I believe Tom Cruise can pull off everything else about Reacher. My objection is his Reacher would essentially be a role he's already played: Ethan Hunt.
UPDATE (Jan. 9, 2013): My objection was unfounded. While Tom Cruise's Reacher benefited from his having played some of the most memorable movie characters, his Reacher did not remind me any previous role specifically. Here's my full review.