I have recently attempted The Long Earth by Terry Pratchett and Stephen Baxter (which is the first of 5 books) and I made it about 2/3rds of the way through before I gave up in boredom. The premise is that one day a device is invented that allows people to access a seemingly infinite number of parallel earths, but humanity never developed on any of them.
This should be the set up for some very interesting stuff, off the top of my head - how do you control crime? How do you manage pioneering these new lands given the limitations (what you can carry, no iron) but also modern design and manufacturing? What are the implications for society, both for those who leave and those who stay behind? This is all the sort of stuff that Pratchett is usually very deft at. Unfortunately, although he gets top billing his input seems to have been minimal.
What we're left with is a meandering and fairly dull piece of prose, repeatedly scene-setting without interest or direction. I'm pretty sure that, had this been Pratchett's project the 2/3rds of the book I read would have been condensed into a couple of chapters so he could get on with more interesting stuff.