Alright for some reason I seem to be too stupid to quote, so I will just post my reply here.
I was really refering to the Wii game, and the boss battle against Bowser was one reason for that, but not the only one. I think even for a Mario game it is nice to have some story, but it must be done the right way. I really liked it the way it was in SMB3 and SMW. You never had story elements that detracted you from playing the game, but there was some backstory and because of that, what you were doing felt far more "important" and towards the end, the games even got a bit scary because you felt the threat of Bowser.
NSMBW did quite a good job at giving these feelings back, and the reasons for that were the last boss fight, the Koopa siblings and the maps. In SM3DL, I don't even know if these enemies in the airships should be the Koopa siblings or whatever, and the maps are really too straightforward. The final boss fight was actually pretty interesting, but as seth said, it didn't feel like being a threat.
And about the difficulty again, I don't know if you are refering to me Mr Kahn but when I have written my first post, I was already at the start of Special World 6 and now I am almost done with Special World 7. I have to say that there were two levels in World 7 (7-2 and 7-4 actually) that took me a bit longer to finish, but that was partly due to me wanting to collect all star medals in one going and also because of a lack of concentration. I hope there will be some more levels of that difficulty in World 8, and that the last level of all will be difficult to. But I already heard that the last level isn't as difficult as the perfect run in SMG2 which I finished, so I am not expecting too much, but that's alright for me.