My thoughts on Bardem: He's got the right "bearing" to pull off Roland. He can definitely do the strong, silent badass, as evidenced by No Country for Old Men. That definitely weighs in his favor. He's also not "Hollywood Pretty", which is a good thing.
The only issue I have with him playing the part is, thankfully, correctable... in my opinion, he'd need to lose some weight to play Roland. Bardem's sort of an imposing figure. Not in an action hero huge muscles sort of way, but the guy looks like he's bigger physically than I picture Roland. Roland always struck me as being on the thin, tall side. Very strong, but more "wiry" than muscular.