Hell yes it is! Lock yourself in a dark room, grab a good pair of headphones and prepare to get your adrenaline pumping. Enemy Zero induces panic like no other game i have played. As you already know, the enemies are invisible and you can only rack their position by a "beep" sound. Not to mention your gun takes a few seconds to charge and then discharges after a few moments, so you cant just blast away. All this coupled with the limited save and load mechanic adds to the horror.
It's a strange mix of FPS, myst style puzzles and fmv gameplay. The game is not for everyone, but those who like it LOVE it!