I never found this game to be as frustratingly difficult as the other reviewer. There are a few parts where you do some adventure-game style puzzles and those can be a little tough to figure out.
It offers real choices which affect the storyline towards the end. It has great pacing and really breaks up the combat very well, which most FPS games at the time did not do. Wish there was a way to give this 4.5 stars. It deserves better than 4, but it's not perfect. I found the giant-robot sections less fun than the FPS, though it was still enjoyable throughout.