Ewan's change (spoiler)
His demeanor upon returning home was completely & totally unrealistic to me right off the bat as it was presented.
PTSD isn't something that makes you go from being an angel to a demon with the ones you love be at the drop of a hat. Especially not first returning home from the war. It's more insidious than that. It presents itself subtlety at first with small things and then grows into big explosions like the one he displayed upon entering the house right away. This was either poor writing or bad editing on the part of the filmmakers/writers and so unrealistic it took away some of the enjoyment of the film.