This video compares the original Metal Gear Solid with the scan lines featured enabled and disabled.
For the uninformed, scanlines were added through the 2.0 patch as an optional setting. This feature mimics how the game originally looks like when played on a CRT television set.
You can find the video comparison below:
As you can see, the scanlines make the Master Collection version look more like how you remember the original on a CRT TV. The filter does make the visuals darker, however.