I did wind up buying the game, and now I'm 13 chapters in and really enjoying it. The game opens up a lot beyond what you see in the demo, bringing in elements like a grappling hook, a bow & arrow, enemies with body armor, and a large area of town covered in toxic dust that you can only stay in for limited periods of time. If you're daring, there's a lot to discover in the dusty areas, which offer some open world elements alongside the more linear parts. There are also some extended climbing sequences a la Uncharted, but much more tense due to your limited grip strength.
The encounters with mobs can be harrowing, since you have to identify the biggest threats and neutralize them first, often with no bullets in your gun. And if you do have a bullet and shoot a gun wielder, one of his buddies may very well pick up his gun and shoot you with it. Each of these mob encounters is like a deadly puzzle to solve, though you will use many of the same tactics in each one.
The graphics and controls aren't super polished, but they aren't clunky enough to get in the way, either. And the graphical filters are very effective at conveying the bleakness of the environment.
It surprised me how much of a Manhunt vibe I started to get from the game after I got further in. As a fan of that series, this was a pleasant surprise. In fact, I'd say the game ultimately feels like a cross between Disaster Report and Manhunt, with a sprinkle of Uncharted thrown in.
For me this is definitely worth $15, as I must be 5 or 6 hours into my first game with no end in sight yet, and I'll likely play through a couple more times to try the higher difficulty and try to help all the survivors. Glad I took a chance on this one. A solid 8/10 from what I've seen so far.