I am going to review this as a literary work only and not a s a guide to salvation. The book is worth reading for two and only two reasons. First,it is continually referenced by other greater works because every literate, English speaking protestant was familiar with it for two centuries. Second, because it in certain ways resembles the Divine Comedy in being a description of a journey that is overtly a parable of the journey from damnation to salvation, and being massively inferior to the Divine Comedy in every way, it helps to illustrate what makes that other work great.
The work lacks literary merit in all respect, except that some of it's imagery such as the Slough of Dispond and Vanity Fair is highly effective visual allegory. However, the book often descends into overt preaching and finger-wagging and regularly confuses a parable with a sermon. The verse in it is notable for its mediocrity and the prose style is for the most part poor. It is really a picaresque and does not have the grand sweeping movement of the Divine Comedy. That is unforgivable in a work with "progress" right in the title.
A second part was written, almost certainly for the money and it is either repetitive of the first or confused. It then devolves into a shambles. There is often a confusion and an inconsistency in the use of allegory and multiple characters progress in different ways and in different times, which destroy the thematic message.
Overall quite bad, but you will love the Divine Comedy even more. Don't give in to seventeenth century hype.