Stedman has followed what seems to be an increasingly popular route in modern literature of positing 'non-academic' theories in the guise of works of fiction. Whether you enjoy this book or not will largely depend on the extent to which you buy into this approach and also the particular theory/speculation that is narrated.
I, for one, enjoy this particular medium for learning (or being inspired to learn) about historical times/figures etc. And this book offers an excellent exponent of the art.
The essential plot is somewhat tongue-in-cheek yet undertaken with a level of seriousness that enables the reader to suspend disbelief. Michelangelo Merisi da Caravaggio has been rescued from imminent death by the Tralfamadorians - an alien race who have a fascination with the painter and his works. These aliens want to uncover the mystery of C's death which is postulated to be a murder case. The fascination the Ts have with human quiz shows has led them to believe that Stephen Madden (read Stedman - partial anagram but obvious allusion) - a winner of various quiz shows specializing in the life and times of Caravaggio - is an expert, or rather 'the' expert on Caravaggio and thus best placed to help them out with their investigation. Of course Madden lives four hundred years on from C's death. So, Merisi is sent, by the aliens using time travelling technology, into the future.
The rest of the book involves Madden being sent, via the time machine, into the late 16th/early 17th century to interview key figures in C's life and back again to the present to verify things with Merisi - who invariably causes mischief in the present while Madden is time travelling. This narrative keeps things ticking over nicely simultaneously giving us insight into post(or late)-renaissance Rome (as well as Malta later on) and providing amusing observations as to how things have changed since Merisi's day.
In the case of the latter aspect (contemporary vs past comparisons), as a reader, it helps to be British in this case. There is various witty commentary on British culture and politics including an extensive conversation that Madden has with Merisi on the sense in which the present British parliamentary system is democratic leading to utter bafflement in Merisi.
Ultimately, while I very much enjoyed this book, I suspect that its market may be narrow - probably it best suits British Caravaggio neophytes (like myself). Being British (or familiar with British culture) is somewhat essential to get the humour here, being new (but perhaps not absolutely ignorant) to Caravaggio's life and times is also probably important. There are many points where Madden is claiming to uncover interesting factors, *SPOILER ALERT* e.g. that Sforza may have helped Carvaggio escape from the Maltese prison of the Knights of St John, that I suspect are not so surprising/worthy of being considered a great revelation - the recent Italian film of Caravaggio's life in fact portrays this very act. To an expert, such 'insights' might grate. We also must hope that the recent purported finding of Caravaggio's body doesn't shed too much unequivocal light on the painter's death so as to render this "who dunnit!" redundant. An (academic) expert might, nevertheless, enjoy a 'light' but humorous read regarding C's life and times and it should appeal to the fantasist who might put themselves in the role of Madden living and sensing the glories of late 16th century Rome.
So, in a nutshell, if you are British, or share a British sense of humour, and are interested in Caravaggio, buy it! Oh yeah, and in answer to my title poser - I don't think they will make the film because its market may be a little narrow as mentioned. They tried it with "Timeline" and it didn't work as a box office hit or as a film of integrity. Crichton's book focused on the historical period, the film focused on a "time travel flick". Any such film of Stedman's book would have to focus on "Carravaggio's murder" - this is not a science fiction book!