EMH, Tomalak301, and Skywalker agree that Browder was wasted, but he was the catalyst for the story's whole climax. His death forced the Doctor to confront Isaac's assertion that he and Jex were "both good men who just forget it sometimes." America, he told us, is a land of second chances, and they call the town 'Mercy' for a reason. By entrusting the Doctor with protecting the town, he indirectly helped the gunslinger find his own redemption. Browder's character filled in all the exposition necessary to understand the points of the story: mercy, second chances, and redemption.
I love Ben Browder, but while he didn't get enough screen time, his every word mattered.
Certainly his character was hugely important, but I was just hoping for more screen time for him, that's all. Browder did well with the role, though. Honestly, I could have done without the Ponds at all here and given some of their screen time to Isaac, expand on him some more and make him more of the 'companion' of the episode.