This isn't exactly an easy book, but it's not as difficult as some other classic works of modernist literature. The language and writing aren't hard. Charlie's rant about Bolshevism is about as difficult as things get:
Even an organism is bourgeois: so the ideal must be mechanical. The only thing that is a unit, non-organic, composed of many different, yet equally essential parts, is the machine. Each man a machine-part, and the driving power of the machine, hate...hate of the bourgeois (4.65-66).
What's tough is that the book is so focused on expressing D.H. Lawrence's feelings about the modern world (modernity) that plot and character—you know, those things that make novels fun to read—get shafted. Sure, there's lots of detailed exploration of how people are feeling, but it's hard to get invested in any of the characters. They're stand-ins for philosophical ideas rather than attempts to represent real people. And that's not bad—lots of great books care more about philosophy than character. But it does mean that you have to put in a little more effort.