I've been thinking about this question for a few days and I'm not sure what I have come to. I was playing the new DMC game earlier, I played it start to finish and it was absolutely tip top, straight up fun. Every 5 levels, I knew I'd get a new boss fight, and I was excited to see how it'd turn out. I was never dissapointed. I won't explain them all, but if you've played them, you'll know what I'm talking about. It's the same with Dark Souls. I'd drag myself kicking and screaming through that game because the sheer fun in taking on these AMAZING looking bosses, with such diverse strategies was such a thrill.
Then I think about more "Boring" and "Challenging" boss fights in the past. The mind harkens back to things like early Final Fantasy games. I always remember in FF9 when you had to fight Beatrix. It wasn't fun. IT was just something you had to overcome to get to the next bit of story. I think about the boss fights in DX: Human Revolution. They were terrible, but I got through it because I wanted to see the next bit of narrative. Maybe that's it? Maybe games that focus on narrative suffer because they throw in an abitrary roadblock to gate progress? It's kind of like that in Persona 4, I guess, except the blend is a bit more subtle, and it's a bit more enjoyable than a rote "This is a thing you have to beat".
So where do you guys fall on this situation? Do you think that boss fights should be a cool thing to reward the player for getting to X point in the game? Or should they be more of a wall that you have to get over to get to the next bit? I'm sure you'll all come up with certain moments which marry the two together, and that'd be great. I'd just like to hear what people have to say about it!