Why did Eureka feel more fun to you?

Personally, I think they're the same. They're boring unless you're grouped up with friends chatting away while you grind mobs down. People are happy with it for now because it's new content but they'll get bored again once they've got what they want from it.

I guess the one advantage Eureka had that I've seen others mention is that it was essentially a large wilderness. Bozja is a warzone. Which environment is more pleasant to be bored in? The wilderness, of course.