Days Gone is one of the greatest sleeper hits in my gaming life, lol.
I also picked it up on steam sale with zero knowledge about it. I fired it up and thought it was meh for a bit but had fun enough mechanics to stick with it. Once you get to a certain part of the story which I would say is probably a good 20 hours deep, it kicks from average to epic. I've had a blast with the game and I'm currently trying to hit 100% achievements.
The story really picks up in the second half as do the characters. While I initially thought the main character was forgettable (kind of reminded me of Brandon Frasier from the Mummy, lol), you begin to feel for him more in the second half when it takes a dramatic turn.
The actual mixture of zombies to humans were great and enjoyed the stealth elements a lot even if they were pretty basic. It just has a satisfying feel to the way everything is performed, even if you get the exploits down pat. I also have to say, taking down hordes is one of the most satisfying gaming elements I've ever experienced. The game is superb and I'm quite disappointed that there is no sequel in the works. It totally caught me off guard. For those that probably didn't like it either played it on PS4 and in a buggy state or just didn't give it enough time (which I can see happening). I've just experienced it pretty much bug free and got to the point where the story kicks into overdrive and then you don't want it to end.