I was able to catch an advance screening of this last night and really liked it, would easily rate it right up there close to SPR. In fact, I might call it the Japanese WW2 theater-version of SPR. The battle scenes were extremely immersive and had me feeling like I was right there due to all the noise & chaos.
The movie spent an unusually long time establishing the backstory, character, family, etc for Andrew Garfield's Desmond Doss before he even got into basic training, probably around 50% I'd guess. But it served a purpose to show how his convictions were genuine, leading to his first conflicts among his fellow recruits and his superiors. The actual battle on top of Hacksaw Ridge in Okinawa took up a surprisingly small amount of runtime compared to the rest of the movie—just a guess but it might have been about a half-hour or so, maybe a bit longer but definitely not even half, at most a third of the movie.
I don't think one really needs to be a Christian to understand the Desmond Doss character, as most of it is explained in flashbacks, but being raised as a Protestant Christian myself (I'm still Christian, but not as "denominational" as I used to be), it definitely helped me to further connect with and respect the character. At first I thought he was going to be one of those "holier than thou" *****ebags, but as the movie progressed, it showed not only why he believed what he did, but he had his own experience that formed & cemented his conviction to never touch a gun along with his later aspiration to be a combat medic. And his conviction definitely made for some harrowing moments in the battle scenes as well, where he was in the thick of the action and had nothing but his wits and medical supplies against the merciless Japanese soldiers.
As far as the cast/acting went: Andrew Garfield did a very convincing job as the self-convicted "conscientious objector" (though I'm not entirely sure that it was a quite Oscar-worthy performance and don't see it as a given that he'll be nominated) and Hugo Weaving was really good as his semi-crazy WW1-veteran father. Vince Vaughn as a sergeant initially took me out of the movie (mostly on account of just being Vince Vaughn) but he played a great character and stole a lot of scenes with some hilarious lines, especially early on when he was yelling at the new recruits.
9/10 for me, and definitely worth watching on the big screen! And although I think it's still accessible for non-Christians, I think Christians will probably understand the movie better (or at least in a way that the non-Christians won't).
