They have been known to cause some people problems like headaches. They look amazing visually and were a lot of fun. It's not really a type of game I would play but it was interesting to see a warrior of light tackling that a few times with FF mechanics. I could appreciate the story too because a kid would dream that a small hole leads to something like that before they understand the world better.
Alliance raids usually aren't difficult after the first days (like any content), because of item level increases and people understanding the mechanics better or having seen guides. I remember the first time I did it, 2 alliances wiped and ours had to take the boss alone. I think we didn't successfully clear the final boss either.
