The PlayStation version is quite different from the PC version. Some major differences are:
The graphics - A lot lower resolution, every is much smaller.
No cutscenes - The only cutscenes are the major plot ones, mission briefings, etc. There are no Echo Sector cutscenes.
"E-mail system" - To make up for the lost cutscenes, there is an "e-mail" system in place of where the killboard would be. Basically, there are just text transcripts of the videos with a lot of neat other new material.
Other small differences:
The last mission, where you blow up the Vigilance Platform core, is on a timer.
There's a bonus final mission where you can talk to the development team of the console version, it's pretty fun.
I recommend getting the PSX version just to see the differences.