I don't care if the film is like the books or not, it's unimportant. I only care if they make a good movie.
The Bourne Supremacy and Bourne Ultimatum don't follow the books at all, and no one on message boards ever complain.
Even if you don't like Cruise as Reacher, he's not gonna play the part for 17 movies. If it's successful, there will be more movies and more actors in the role.
If it's not successful, several years down the road Rob Cohen might make a Reacher movie with Tyler Perry.
Both of you are right. It's an adaptation, it can't be exactly the same and the existence of this movie doesn't mean that the books stop existing and being good.
But as a big fan of the novels, despite still wanting to see this and expecting it to be a good movie, I can't help but be disappointed that they have cast someone so totally and utterly unlike the guy in the novels in every way. It's not just height, it's looks, demeanour, attitude and personality. I do like Cruise as a leading man and I expect him to bring something interesting to this role - I just wish he'd kept it for another character!
As regards Bourne, I suppose the difference is that the books were nearly 30 years old by the time the movies were made. They were very much set in the 1970s, as I recall and would have been period pieces had they been adopted for the big screen by Damon and co. And by and large, period set action movies don't succeed. Not to mention that most people would have forgotten the original novels.
OTOH, the Reacher novels are fairly recent and for the most part won't need a lot of updating (indeed, One Shot, which this movie is based on) was written in 2005 and there have been one a year ever since.
But hey, here's hoping it's a good movie at least.