I've been reading New Grub Street in bits over the last months, and I can't explain why I'm giving it five of five stars at GoodReads, but I'll try.
The reasons I liked it:
I felt for the characters, even the ones I wouldn't have expected to.
I found the setting, London's literary world at the end of the 19th century, fascinating.
Gissing's a keen observer of human nature and how it's effected by money, and especially by the lack thereof.
Though some reviewers say Gissing is humorless and his style is only functional, I laughed a number of times at phrases I thought well-turned.
The reasons I wouldn't expect to give it five stars:
It's depressing. See my previous comment about human nature and money.
It's long in a way that tempts me to edit it. It's not exactly redundant, but it's leisurely in a way that modern writers are right to avoid. And yet, that could go under the reasons I liked it, because it did not bore me.
Perhaps the strongest recommendation is that almost everything Gissing says about publishing in general and writers in specific is true today.
I decided to try it after reading The 100 best novels: No 28 – New Grub Street by George Gissing (1891) | Books | The Guardian. If you're tempted to read the book, don't Google it much, or perhaps not at all—almost everyone gives away what happens in the last chapters. Alas, that's even true of the Guardian piece, but it doesn't dwell on the end, so you might forget it by the time you read the book.l