From academic or high-brow critics you'll occasionally read whines that Dickens was too broad in his literary effects, too exuberant and showman-like, too crowd-pleasing with his characters, and sometimes sentimental in his situations. Translate these complaints as, "too popular to be good." (The same elitism undervalues modern writers like Stephen King or J. K. Rowling.)
It IS true that Dickens' writing was sometimes sloppy: he wrote fast, for newspaper serials, with no chance to go back and edit things. By nature, he was not primarily a language stylist. He was a story-teller. Terrific, memorable characters! Some of the sentiment in his work comes from his era - oh! those lace-valentine Victorians! - but much from his own heart. The young boy who had to glue on labels in a Victorian factory knew the dark side of the Industrial Revolution.
In his own day The Pickwick Papers was smashingly popular comedy (the sisters in Little Women play Pickwick Club). Nowadays, some of his most popular books are: Oliver Twist, David Copperfield, Hard Times, A Christmas Carol, and Great Expectations.
There have been countless films made. On-stage? I've gotten to design for Edwin Drood, there are famous versions of Nicholas Nickleby, there is the musical, Oliver! and never forget that perennial fund-raiser, upon which so many theaters depend, A Christmas Carol. Scrooge alone would make Dickens immortal.
The Mystery of Edwin Drood, WaterTower Theare, set design Clare Floyd DeVries
Yet... Why still so popular?
Basically, Dickens gets it. He understands us and our plight. He could be writing today - as this famous beginning from A Tale of Two Cities shows:
"It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, we had everything before us, we had nothing before us, we were all going direct to heaven, we were all going direct the other way..."
Just read today's headlines.