When you mentioned Metal Gear Solid, I knew this game was for me! Making such a game that just works with a browser is awesome! I just had a slowdown on the penultimate level when the camera went from fixed shots to movable shots.
I have two suggestions: that the camera field have two shades of green, one shade for the cone in the air and one shade for the disc on the ground. This will allow the player to be more accurate, because the cone in the air is less fatal than the disc on the ground. Another thing: we do not see the field of vision of the enemies. However in MGS2, we saw it on the map, with several colors even, depending on the state of detection. It can also be justified to scare the player more.