This is a little different from some of the other, earlier tales, in which characters were either totally good, to exemplify everything that is good in the world, or utterly corrupt, to exemplify that which is evil. I don't fault him for this. It was a literary device that he used at the time in order to explore issues of the age, but it is refreshing to see something a little different.
Second of all, the themes he uses of duality and redemption are multifaceted. Charles Darney was willing to redeem the sins of his fathers, despite the fact that he was not responsible for them. This noble act of redemption, which meant facing the guillotine, was foiled by Sydney Carton, who died in Darney's place. This act served a dual redemptive quality. In it, not only did he redeem himself, but also the name of a family he had absolutely no connection to.
Some have likened his act of redemption to Jesus, but I think that there is a problem with that analogy because he was not just dying for the sake of another, but also for the sake of himself. It is an imperfect allegory. This was done purposely to humanize the redemptive act. In short, the final famous phrase has more impact because it he is it is done by someone who is so fallen, that losing his life is his only salvation.
Dickens is, despite his revulsion for the baser acts of the revolution, sympathetic to it and it shows. One of my favorite scenes is when Dr. Manette's testimony, written during his time at Bastille, is read. In it, he gives an account of the events that led him to be falsely imprisoned in the first place. The description of the treatment of the serfs is pretty bleak, and surprisingly explicit considering the time period in which it was written. But, my favorite line in the whole book can be found in it, as Dr. Manette leans over to treat a young man who is mortally wounded.
The young boy tells Manette, "We common dogs are proud too, sometimes."
It contains some powerful imagery and interesting characters. His wordy, overly descriptive Victorian style, which is sometimes a hindrance, works very well giving us a sense of the period through language. The dialogue was impressively handled, nuanced and consistent with the individual's characterization. Darney, for example, is properly reserved and aristocratic, despite his humility, while Carton is properly roguish and snide.
This isn't a real review, because I am not qualified enough for such a task. But I hope that my thoughts on the subject will encourage someone to pick up the book and read it. It really does deserves the title as one of the great English classics, but that has already been determined by those much greater than I.