I think people are comparing this to Negima too much, they're getting themselves hyped up for something really big. I was pretty satisfied with how Negima ended despite the fact that I was sad about it too, but not so much that I was expecting this to be a direct continuation of it.
Maybe the reason why some people seem to be ignoring how great this is is because of the difference in main characters?
While both Negi and Touta are cheerful there's still a major difference in their personalities, as well as the fact that Touta lacks the major motivation and goals that Negi was so easily able to grasp to push himself ahead. And if you pay attention it does become clear that Touta has the pure talent that borders on genius that Negi had, but when put together with the difference in ages when comparing their abilities alone is probably a step down from previous readers of Negima.
So in the end the people that are unsatisfied with UQ Holder are probably just comparing Touta to his genius grandpa and getting disappointed when he isn't matching up to him already.
Though in my personal opinion I think UQ Holder is turning out to be just as amazing! Right from the start the main character becomes immortal, therefore introducing us to other immortals along the way and showing how life has changed for people after magic was introduced to the world. I personally think that things are just going to get better from here; this is technically a sequel to Negima even if it takes place far in the future, so I think that should be a sign in itself that events are just going to get better and better along the way - in the beginning Negima itself took some time to heat up in it's story-line, but after things started to escalate slowly it became more interesting and really sucked you into the story.
Right from the start Touta becomes immortal, but even then his past is mostly a mystery so there's no way to know if he had already known magic to an extent or even if he had/ has any connection to other people besides his parents, Yukihime, and the village where he had lived for two years. It could be speculated that he has just as much talent as his grandfather -Negi- or that he could have even excelled just or almost as well academically. But now that he's immortal his aging seems to have stopped completely, and it could be said that he is only lacking in motivation where it concerns gaining strength.
Overall, I imagine that UQ Holder will become more popular as time goes on and the story continues.