I had to read "Middlemarch" for a Victorian literature course, and I approached it with certain trepidation: it's a tome, for a start, and by the time I braved it, I'd heard pretty much everyone in the class muttering about how dense and difficult it was. I had that reaction, too, for about 100, or even 200 pages. But I fell in love with it slowly. You have to almost re-learn how to read when you approach a novel like Middlemarch; it was not written to cater to short, wandering attention spans. But the brilliance of this book gradually reveals itself. Eliot is subtle and serious, but she is also witty and very humane, and in "Middlemarch" she tackles so much: science, art, religion, politics, love, morality.
I noticed by the end of the course that everyone who had previously been whining about this book had come to feel a certain sense of awe toward it. "Middlemarch" certainly demands a lot of time and thought to fully appreciate, but it's not difficult to understand why this is considered the great Victorian novel.