Because their traillers where total BS. The game is fun, but actually the graphics are way worse than advertised. I'm not talking about PS4 and X1, the PC version on Ultra isn't much better than GTA V (except resolution, AA and reflexes), that is a PS360 game. Texture are pretty bad. Despite that, the optimization is terrible: PS4 at 900p@30fps, X1 at 720p@30fps and the PC version is ridiculously demanding, it's actually way more than Metro: Last Light, even if it looks like garbage compared to Metro.
In the end, lightning is good, reflexes are good, textures are bad, cars are downright horrible (GTA V has better car models). About the game itself, it is good and have decent mechanics and I recommend you. The game itself doesn't deserves the hate, but the fake traillers that were shown until the launch were just a lie to consumer. Game: 7.5, Ubisoft: 2.
