Leaving a theater is a complete douche move to begin with. Why even go to the cinema in that case? If its that bad that you leave, when why the fekk do people go watch it if theyre not in to that kind of a movie? You should know what it is about before you buy a ticket, or else you got yourself to blame. I have personally never ever seen anyone leave and dont understand why the hell you would leave in the first place. Just finish the movie.
It may be offputting for some as this kind of full lenght movie have never ever been done before with a higher profile and big budget. Its high fantasy sword and scorcery all the way. If you expect to see another LotR youre way off point and will surely be disappointed.