Steins;Gate 0 takes place right in the middle of the True End of the original visual novel. It tells the story of the broken man. The man who is not the one to be with her. But he is the one to make the other one be happy with her.
Steins;Gate was supposed to be very dark and dramatic. Unfortunately, there are some slice or light-hearted moments which are not really needed. But still, the game is amazing. The new cast is very interesting. The interlacing of all the endings is out of this world.
I would be careful in recommending this game to S;G fans as there is a big chance they will not really like it.