I think the sequel holds up well to its predecessor, though I have to admit, I don’t like UQ Holder as much as Negima. The reason for this is very very very very simple.
I’m a fan of romance. While I can’t deal with straight up romances (a girl I dated awhile back tried making me watch her romance movies and I feel asleep. They were a total snooze fest.), I still enjoy anime/manga/books whatever with heavy romantic themes.
Negima satisfied my need for romance, while maintaining a certain level of badassness. It had an excellent blend of romance, action, comedy and fan service rolled up into a nice package of pleasant to look at artwork.