I finished Generation Zero last night. Bit torn on how to evaluate it. The early to mid-game was really good then it kind of tailed off.
At first all the machines roaming the world were really threatening, you constantly felt totally ill-prepared to take on the threat they posed - just like a barely-trained teen protagonist would be. So, I was creeping everywhere, tensely listening to the noises of machines passing, trying to figure out where there were, hoping I wasn't spotted. I only enaged when I could plan the encounter, set traps and ambushes and have a route of retreat open. Great atmosphere!
Then, you get some more skills, weapons and equipment and the bulk of the machines become enemies you can take on okay (albeit they can still kill you very, very quickly). The game introduces some hulking monster machines that are still tough(ish), but I found they were more tedious ammo-sinks than real threats for most of the mid-game. I was avoiding them because I couldn't be bothered fighting them rather than because I was scared of them, which was not the same in terms of tension.
By then end-game it was all getting a bit repetitive, to be honest. You have to find region quests in the same maze of bunkers with the same assets, almost the same layouts and the same "find out how to turn on the power" set-ups. You notice that all the houses, all the towns, all the buildings are all the same everywhere. And enemies just appear in bigger groups. I got through the last few hours by just hacking a stray low-level enemy whenever I saw a group and running past all the others as they started fighting. Kind of cool that you could avoid combat so consistently (the game only very rarely forces you to fight if you don't want to), but also a bit of a reflection of how I was getting tired of emptying clip after clip into the same machines.
So, really good for a while, fairly enjoyable for a while after that, and a bit of a slog by the end. About a 6.5/10, I guess.