True Ending To E.Y.E Divine Cybermancy
So, there is this doomsday cult thing in real life called "Heaven's Gate" Founded by Marshall Applewhite, they believed that their souls were trapped in the human body and dying was the way to achieve a higher level of existence.
In 1997 24-26 of march, 39 members of this cult committed mass suicide by drinking cyanide. They were made to believe that behind the comet "Hale-Bopp" which that night passed by earth there was a spaceship that had come to take them to another realm. This all happened in France, E.Y.E is french too.
Now here is the intresting part, there is alot of referrences to Illuminati in the game, such as the name implies "E.Y.E", and the pyramid on the logo, and also the many eye and pyramid referrences we can see in the game, not to mention that the achievement "Hypnotic Gate" for getting the Hypnotic Gate ability is all red and black while all the other achievements remain red and yellow, or just the fact that there is an achievement named "Illuminati".
Now here is my theory, You wake up in the cave in the beginning of the game when the rest of your squad was killed, so were you, you just dont know about it yet, as you continously keep coming back to the dream sequence with the two gates its usually the night gate you enter. Even though your physical body was killed in the cave, your soul was freed, and still lives on through the game, meaning that the game is a dream. so night gate = sleep = dream.
HOWEVER, in the ending, maybe you haven't noticed but its the sun gate, not the night gate you enter. The true gate, the gate that will continously keep sending you back to the beginning of the game until you manage to find the fourth and true ending achieved by speaking to Circe, the ending with the floating island. Hence the name "Heaven's Gate".