How does it measure up to the N64 port? Well, it's not far off to be honest. The N64 version uses the Expansion Pak to enhance the colour palette and frame rate, but it doesn't boost the screen resolution so the game does look a little blurry. Indeed, when compared to the PS version it looks very muddy indeed...but when you notice the much more impressive and varied geometry in the levels, you'll see where the N64's extra grunt is being employed. Examples of this are evident from the get go - in the first proper room (through the first set of doors), you can clearly see that the far wall has been totally stripped of any columns or boxes on the conveyor belt in the PS port. Likewise, in the second room, the explosive barrels are gone, and the moving boxes on the track along the ceiling are expelled from the the PS. A bit further on little more details such as moving scenery and the secret rooms (and hints) are absent. Also, in the room with the shootable switch, the fan in the ceiling has much less detail in the PS game. Oh, and the doors in the N64 game open with a vertical split down the centre, while the PS doors open vertically upwards from the floor.
There are other differences too. One of the most obvious is the inclusion of FMV sequences in the PS version, but which are absent from the N64 cart (clearly due to space issues). The strangest difference (for me at least), is the way that the PS version lets the player continue through the stages as if they were one gigantic level, and simply have a loading screen when the next section is prepared (Half Life on the Dreamcast did something similar, incidentally). The N64 port doesn't do this - instead splitting the levels up into totally separate areas with mission objectives in each. This is shown in the video where at the end of the N64 section the player goes into an elevator and is then sent to the next level, whereas in the PS port the player enters a doorway opposite where the elevator would have been and the mission continues after a brief loading period. But enough waffle. Have a look for yourself: