I have finished all four episodes and all I can say it's that it got better and better with each episode. The campaign is a long one (23 hours of gameplay on steam) and it has lots of things for any RE fan to taste. You have the classical over the shoulder handling of the gun and those damn mutants all over you. The game is truly amazing (though it has some boring sequences), but the characters are amazing. You play as Barry and Natalia, Claire and Moira, each one with different skills and flaws. There are some pretty nasty boss battles along the way, but manageable. There are tons of puzzles and both characters must be used.
It has, of course, a gloomy atmosphere and that is great.
I replayed it on XBOX 360 and I must say it's better than on PC.