Does a game have to be designed for VR to be immersive?

Yes, the game has to be made for virtual reality to be 3D. If you use the headset with a non-vr game, it will be as if you are sitting an inch away from your tv screen. You will strain your eyes.

Kinda since some electronics need something to make it work better than before

Not necessarily, but eventually there will be some very immersive games coming from the VR side of gaming. It almost begs to go there. I'm not interested in VR YET. I'll get there when they make a game (or I do) that I'd wanna play in VR. I don't know how immersive it needs to be, but i know it has to be realistic. Whats the point of VR if it's not realistic>

Sadly,,,I bought the ps4 VR headset not for vr games but because the headset is the controller. Aiming on it feels so natural and real....HOWEVER..the pixel dimensions of the headset were not high enough to enjoy games on. I was playing far cry 4...it looked amazing...except for the graphics. The screen was slightly fuzzy I could not get it just right...but what was worse were the textures. Instead of fighting enemies I was fighting polygon people. Instead of having faces they just had a blank head...it was very strange. As much as i loved exploring the envirment that way I could not play like this,...and so i returned the headset...which also had a textured screen..which was noticeable at all times