Huckleberry Finn says of this book that "The statements was interesting, but tough", which I think is fair. Several things struck me - the unattractiveness of the main character, Christian, who wilfully abandons his family, and having lost his first travelling companion Faithful by gruesome means then becomes a know-all to his new friend Hopeful; the fact that the metaphors and allegory are about as subtle as a brick (actually, a brick is more subtle - perhaps "as subtle as a Vogon Constructor Fleet" is the simile I am looking for); the fact that when you think you're finished the book it then turns out that his wife Christiana and four sons are going to do the same journey; the repeated use of prisons (as Anne said, write about what you know) and capital punishment; and the fact that the main characters are happy to drink wine without threat of eternal damnation, something that many of the book's greatest fans today would probably disagree with.
I don't think many people actually do finish the book. Perhaps its most best known image is the Slough of Despond, which is actually described in less than a page in its first appearance (page 31 in my edition). Vanity Fair, while a great name for a town, seems to change out of all recognition between Christian's visit and Christiana's. And their children get married off with rather indecent haste.
Two final thoughts. First, the opening poem says some interesting and almost charming things about writing (as well as of course reflecting the writer's views on other matters); I think it's rather nice.
When at the first I took my pen in handAnd my second, much naughtier final thought is this: I kept on reading the dialogues between Christian and Hopeful/Faithful, and wondering what a skilled fic-writer like daegaer or cygny or aramuin could make of that relationship. Ladies, if any of you chooses to try this one, I look forward to finding out...
Thus for to write, I did not understand
That I at all should make a little book
In such a mode; nay, I had undertook
To make another; which, when almost done,
Before I was aware, I this begun.
Well, so I did; but yet I did not think
To shew to all the world my pen and ink
In such a mode; I only thought to make
I knew not what; nor did I undertake
Thereby to please my neighbour: no, not I;
I did it my own self to gratify.