It is a mediocre movie at best and without the back story of Kyle, including his untimely and tragic demise, I don't think it would be nearly as well regarded.
There was way too much in it that made me WTF, Marines were portrayed as bumbling dolts and his spotter was made out to be a coward (Kyle went to clear houses and the spotter said something like "No fuck that, those guys picked the wrong job, I like my life"), calling home on a sat phone at all sorts of ridiculous times, two click first round head shot on his sniper rival, there's more but I don't remember it all.
If it wasn't the story of Chris Kyle it would be a very forgettable movie, but because it is about Kyle it will favorably color many people's perceptions.
I did not read the book, so I have no dog in the movie vs book fight.