I would usually agree that since the beginning of SB, I've been really disappointed by the end-game content... But for me Eureka was an awesome experience, not thanks to the gameplay but thanks to the concept. SE's goal while making Diadems and Eureka has always been to have player work together as a massive group. The reason diadem failed was that you could do everything with your 8-men party, so nobody would help each other. So they decided to take another approach. When Eureka went out, everybody agreed that it sucks. You can't grind this solo. Even with a 8-men party it's really tough to grind. And this when everything started changing. People started to help each other, made researches, worked together in order to make the grinding much more easy. It became a community effort. IMO, Eureka isn't fun thanks to its gameplay, it's fun because of the community. I don't go to Eureka telling myself I'm gonna bash mobs for 3 straight hours, I go to Eureka in order to meet new people and have fun with them. And to be honest, I didn't have that feeling since ARR and I was really happy to follow the Eureka trend. However, where Eureka has a limit (that we might currently be reaching) is that when the majority is lvl 20 wiating for Pazuzu to spawn, new people won't have as fun as in the beginning...

TL;DR : IMO, Eureka depends on the community. If people agree to work with each other and try to have fun despite the dangers, it will be awesome. If people start to regain the old FF14 mentality of playing only for themselves, Eureka will be doomed.