For some unknown reason the oldschool red hardback complete works of Dickens of my Mum's has Oliver Twist and Great Expectation bound together. Why? Probably because they're not that long, and they want to make all the volumes the same size. Why is this interesting? Oliver Twist (1837-9) is from early in his career while Great Expectations (1860-1) is from late in his career. So what differences do we see?
Firstly, Twist is written from a third person omniscient perspective; the narrator sees all, from the streets of London, into hidden places and furtive meetings, and right down into the deepest, blackest depths of the character's souls. Oliver himself, our hero, is an innocent and good-hearted boy who is unfairly persecuted initially due to being a poor orphan born out of wedlock, and later because it suits the purposes of the villains. Twist is set adrift; things happen to him that he has no control over, and eventually a cabal of those who wish him well ferret out the truth of his origins to defeat the conspiracy of those who are villains. Bad things happen to good people, but in the end they get their just desserts as do bad people. Also the dog as well. Poor Bullseye.
Expectations is written as though it is the memoirs of Pip, the protagonist. Pip also begins as a good-hearted boy, but swiftly finds himself doing bad things at the behest of an escaped convict. Following on from this, he is unfairly favoured rather than persecuted; firstly by Miss Haversham's attention, mixed as that turns out to be, and then by coming unexpectedly into property. Pip is also blissfully unaware of his own flaws (at that time; when he gets to writing the memoir some ten years after the main events he has a better perspective) and makes the not unusual assumption that with the money, clothes and bearing of a gentleman, he is indeed a gentleman.
We see more development in the supporting characters as well. In Twist, we see a lot of one-dimensional villains, and two well drawn baddies in the form of Bill Sykes and Fagin. On the good side, most of the characterisation is from one or two physical descriptions or turns of phrase. The most interesting character is Nancy, trapped by loyalty to the criminals she lives among, but wanting to do the right thing. Oliver himself barely exists.
Outright villains are rare in Expectations; Compeyson whose swindles have started the chain of events that Great Expectations is the end of; the violent smith Orlick; and Bentley Drummle, Pip's rival and Estella's husband. Each of them have little actual pagecount but overshadow events in their various ways. Everyone else is fairly well sketched, being a bundle of attributes rather than a broad caricature. Even Jaggers, the lawyer who lurks as the connection to most of the cast, initially the very stereotype of the lawyer who acts for any client who can pay, is revealed to have surprising depths.
So here is what I think is the difference between the two novels; in Oliver Twist people are villains or heroes, and eventually the heroes defeat the villains and, importantly, no one learns anything new. In Great Expectations there are heroes, but our protagonist isn't really one of them, and the villains are defeated, but that's not what's important. What's important is that Pip learns the relative value of friendship and money. Also how the girl of his dreams isn't the girl who exists in front of him. Or anyway, there's my take.
Read These: Because Dickens is hugely entertaining, as well as giving an intriguing view of Victorian values and society.
Don't Read These: If the Victorian novelist thing of long-winded tell-rather-than-show-and-then-show-anyway aggravates you.
Out of Copyright and Available for Free Online: Oliver Twist, Great Expectations.
 I want to say screentime; child of the 70s as I am I see everything as a movie.
 Except for readers who don't know about the Poor Laws or London's criminal underworld.