Pip is a problem: he's a character you like and hate. His harrowing childhood begs our sympathy, while his behavior as an adult makes us embarrassed for him and angry for those he wrongs. That he narrates his own life makes the difficulty no easier to resolve. The hardest part is his own admission of weakness and his outrageous humor, which undercut his lousy behavior.
The true difficulty with Pip is that he's so real. The hero of Great Expectations isn't a bad guy, he just exhibits a very human propensity to not try very hard to be good, even at great cost to others. And of course we're ready to point to evil Orlick, or crazed and vengeful Miss Havisham sitting like a ghost amid material ruins, or cruel Estella, and remind ourselves we aren't as bad as all that, when in fact we (like Pip) treat those we love worse than they treat their enemies.
Dickens' gothic masterpiece signalled the end of his sentimental period and the beginning of his darker, more realistic and mature work. Pip is one of the most realistic heroes the novelist ever conjured, and the first we follow from childhood to adulthood as well as from innocence to fall and back to redemption. This isn't just a story about failed romance, mysterious parentage and rags-to-riches, it's the universal struggle for self-identity and moral integrity with its attendant sadness and pain. What ultimately keeps us on Pip's side isn't his likability but his refusal to capitulate to circumstances and to finallyunderstand the superiority of a life well lived to a mere grasping at supposed happiness.
If you only like books that end with singing birds and "happily ever after," find something else to read. Great Expectations isn't all gloom and shadow, but it isn't a happy book. The end satisfies (the original, that is), and there are scenes of joy among bitterness, but Pip doesn't get a happy ending. Even his reconciliation with Joe Gargery is melancholic, despite their great mutual love. Pip becomes a grown-up the way all of us do, at great cost and without assurance that everything turns out.
Dickens' use of first-person perspective lends an immediacy that helps us identify more deeply with Pip. We laugh with Pip, we cry with him, we hope things will end well and are disappointed but resolute when they don't. And while Pip's journey toward self-awareness is central, it's the goodness of Joe and the mysterious Abel Magwitch which ultimately move us—and the hero—toward renewed faith in the presence of good even where it is not well-received.