Fortunately those aren't too frequent. Weapons are abundantly available and can really do some damage to the enemies. The main ingredient in MGS is stealth. Yes you can kill everyone on the screen, but you'd be better off using stealth and trying to evade enemies. Once you start to engage an enemy an alarm will go off and then more guards will show up, which almost certainly will spell your doom.
Bosses are also readily available.
You will encounter the bosses and then watch a nice movie explaining the story some more. While not too hard to beat, the bosses do each posses a good amount challenge to keep you on your feet. Well I think that it easily surpasses the Playstation version. Enhanced graphics, the inclusion of the VR missions, and an overall greater sense of realism and action. I had a much more enjoyable time playing the PC version than the Playstation version.