I started to comment on the several negative reviews but found the chore not worth it. The problem may simply be the modern reader which one cannot change. I won't list their issues because the culture is to blame. I will just say that the novel is one of the books for the ages, one of the best of the 20th. Century and the big mechanized wars that it saw begin; and the events in the story are believable (including the romance). The romance in the novel has satisfied readers through almost a hundred years, and anyone with any life experience knows love grows in many unpredictable ways. The simple style is Hemingway. Those who just discovered it and choose to criticize it should have known. It is a style, Hemingway's style; and he's good at it. He was a poet at heart who was writing novels. For the lack of description at times it was the poet at work and he had his reasons. Like a poet he left things sometimes vague. It was, I suppose, part of the whole 'iceberg' theory thing.
Another thing that might be in play with negative reviews is the fact that the modern reader is often impatient, with a short attention span. An educator friend blames Lucas whom he says discovered he could entertain audiences with more constant action in his movies. I don't know, but modern readers seem to have a problem with deep, slower, contemplative, and real-life paced fiction. I find it in my own novels which are more popular with older folks (50+) though they are full of action (realistically spread out through the stories).