Replayed it last year and had a blast. Even tried to beat it on the hardest difficulty but I think I only got until the godforsaken computer room in which you have to protect Natalya while she does some computer hacking. Fuck that with a capital F, I moved on to Perfect Dark and kept on having a blast.
Those games are very cool, being objective based instead of full linear afairs. Also it's difficulty system makes for great replayability. Just wish we had more games like those.
I never played the original on the N64 as this game is as old as I am, but this is seriously one of the most enjoyable FPS experiences I've had in a while.