This game is a living piece of history, with all the good and bad that comes with it.
The main issue this game has is that it's not from the world "Doom" and the like comes from. It has half a foot still in the "atari, beep boop, life and point system" ground, and this becomes obvious after trying to 100% any given level. All the maps look very, very similar, it beccomes difficult to tell WHERE you are without the use of the map, and in general it's insanely difficult to play the game to the full potential it deserves.
The vast majority of the secerts are hidden among identical looking walls, gameplay boils down to corner camping the basic ai, and there's really, really not much to say, since the entire game is a basic package with nothing more than basic floor layout with only right angles, and the sound is nothing but muffled sound effects they could pull off at the time.
Despite all this, the game DOES get a free pass simply for being so stooped in history. Without this game, you wouldn't have the vast majority of FPS we have now. If you want to buy this to know your roots, go ahead, but be warned, it's about as odd as a time capsule could be.