TLDR: Don't buy this book unless you specifically want more Matrix fluff or run decker/technomancer-centric campaigns. Go get Run Faster if you haven't already.
I went into Data Trails knowing that others had already said the "good stuff" was missing from it. I kept a detailed report of how I felt about the book. It started off with five stars, and then after the first section of fluff it quickly dropped off. I eventually had to quit reading and come back a long time later to finish up. I am reading it a second time just for the rules, but now I can't even do that.
First and foremost, their talk back in January about fixing up the proofing process back at the end of January (link below) seems to have not gotten anywhere, as there was a parade of errors in the book. It's hard to stay into the reading when I keep coming across them.
Second, I was hoping Data Trails would fill the void of questions left about the Matrix. All it really did was add some things on and provide a lot of fluff. Most of the fluff is good fluff, mind you, but still. And then the end is padded with a re-explaination of the rules.
I'm giving this a 3 if only because there are added things in here that are -fun-, and some are -interesting-. But in all honestly, I'm highly disappointed in Catalyst and will be taking back my pledge to buy their books until there's been a good amount of time to see reviews.
[3 of 5 Stars!]