Nexus is incredible.
If you are into semi-religious space-thrillers such as Event Horizon, then you are going to love this show.
As others have said, it is very different from other Ultraman shows. One of the main differences is that the whole "hero of light" thing is dropped, and instead the role of being an Ultraman is seen as more of a curse, and being the host of this alien not only fucks up your mind, but does damage to your body as well.
In this show, you also won't see any cheering crowds as Ultraman defends the Earth.
Instead you have a corrupt military organization that sometimes try to kill or capture him.
I also want to give this show points for having scary villains. Its quite rare these days to see a toku villain that is actually scary, but the ones in Nexus are really nasty, not in terms of design, but because of the psychological terror that they put their victims through.
So give it a chance. You won't regret it.