Good war novels?

I'm looking for some good novels about what it's like to be in a war. I'm particularly interested in WW1. I guess the books are all about the horror of the trenches, the scarcity and how it would actually feel to be in a battle? Not sure what other themes a war novel could have.

And I'll just go right ahead and say it: I mainly read speculative fiction and have a terrible attention span, so the idea of reading something 'proper' intimidates me a bit.