I love the Matrix. And I really like SR5. I think they've done a lot to really improve the game from SR4.
The Matrix resolves faster and its rules are more consistent with the rest of the game.
With that said, Data Trails is terrible. Its the lightest core supplement book released so far. Not just on page count, but also on crunch. A lot of this book is fluff, and don't get me wrong, I love the fluff in SR. But the Matrix doesn't need fluff, it needs more options. There are only 2 really new things, Deep Dives, where you go into the Foundation of a Host and can control it but where the rules get weird and dangerous and a lot more abstract, and playable AIs. There is also one new Matrix action and the ability to modify electronics, which are cool but I don't feel drastically add to the rules.
There is some pretty damn good fluff in here too. The short story, Body Hunt, is an amazing read and even brings back the classic character Wolf from Michael A. Stackpole's Wolf and Raven novel. But, while the story was a great read, the rules to do what is done in the story are not explained. Though it is kind of implied how to possibly handle it. And another other short story, Corporate Sponsorship has a decker data spike a camera then mark it with sleaze, which makes no sense by the rules. Anyway, this isn't actually important, because I don't think fluff and crunch need to match, but it sure is nice when it does.
The problem is there isn't enough content in this book. It has a lot of sample hosts and NPCs, which I don't care about, because I'd rather buy an adventure book for that content. For a core supplement I'd rather have more options for deckers and TMs for players, which can also give more ideas and options for NPCs.
The worst part is that there are rules for NPCs but not for PCs. No prices for wireless-negating-paint or faraday cages. No rules for writing software. Nothing for how much it costs to have a host. This means that NPCs can have these things, while PCs can not. One of the things that helps GMs and players is the ability to theorycraft and steal ideas from each other. Anything the PCs can come up with, the GM can use and visa versa. But that is not the case in Data Trails as the GM and PCs are playing with slightly different tools. Its disappointing.
There is also a lot of word count dedicated on clarifying core. Which honestly, is lame. I didn't pay $25 to get the same content in core just explained to me again. I want new stuff. Exciting stuff. Cool stuff. I just want pointless part of the rules that really slow down gameplay, like hacking cameras or opening doors to resolve faster while having epic things like data steals be even more epic and amazing. I want the Matrix to be so insanely invasive to the setting that a hacker isn't there just to loop cameras and open doors, but is there to mess people up with hacking, like a mage can with a fireball or a street sam with a big gun. I just want the Matrix to matter. This book doesn't help with that.
[1 of 5 Stars!]