The best single player game I've played in the last 10 years. The graphics are great. Very cool level design. Music...It's perfect for this game! At the "Nightmare" difficulty level, some places are really difficult to pass and this is great for modern games (press "x" to win). The monsters look quite scary and are often scary. This is especially true for knights and barons of hell. There are many secrets, just like in previous parts of the series.
I would also like to say something about the plot and atmosphere. I found the plot interesting and the motivations of all the characters were clear. I really liked the various articles about the UAC and the history of the many places and monsters that can be found while playing through the game.
The game has a good tactical component, and this applies not only to moving around the battlefield and choosing priority targets to kill. Here you can choose from what and with what modification of weapons to fight.
For me personally, the game is almost perfect. I just wish there were more levels.