It seems to function better than the original release but it still has a number of problems, though the crashes appear to be gone.

1. The correct Xinput controls (including the triggers) aren't set up by default. This is a minor annoyance.
2. The max internal resolution is pretty low, though substantially higher than the PS1 release.
3. There isn't widescreen support, so the image is letter boxed.

There is a mod that apparently fixes these issues but I haven't tried it yet.

This is probably the easiest way to play MGS1 on the PC at this point.

Yeah, honestly it's not a bad port. It had to cut some stuff like vibration and motion blur effects because they relied on some specific PS1 architecture quirks that you couldn't easily emulate on PCs of the time and it was relatively tricky to get it running on modern machines, but nothing unusual for 20 year old PC ports. The only issue that you couldn't really fix with the use of fan-made mods and tinkering were the FMVs sequences during cutscenes, but otherwise you could run through the entire game with few issues and it wouldn't be that different from what you would experience playing the original on PS1. GOG version plays fine right out of the box and it fixes the FMVs, so in my view it is easily the second best way to experience MGS1 (and the best and simplest legal option on PC).

Pillar boxed, Pillar box is for when the image is not wide enough to fill the screen (4:3 in a 16:9 screen, 16:9 in a 21:9 screen), letter box is when the image is not tall enough (16:9 in a 4:3 screen).

I remember playing the original PC version with fan patches and the game's frame-rate tanks during cutscenes where the subtitles appeared and the only solution was to turn it off entirely and apparently the GOG version fixed the that issue. The only issue so far that remains is the game crashing with Software Render used instead of the hardware one from the GOG ddraw wrapper.