One of those things is the different ways that immortality is imagined in the series, and the varying strengths and weaknesses of different kinds of immortality. Touta as the MC has one of the strongest types, granted to him by Evangeline, and it varies in type and efficacy from there.
My other new favorite thing ever has showed up in this manga, and that's the Gravity Blade that Touta wields.
The Gravity Blade appears in the test that Touta and Kuromaru have to take as entry into the organization of UQ Holder. It's a brief 'sword-in-the-stone' moment where Touta is prompted to draw it from it's holding, something that has been tried time and again by countless would-be wielders.
Touta gets it on his second try, after noticing the dial that sets it to light or heavy. Which is one thing I'm happy with, that they didn't draw out this training period overly much. The Gravity Blade itself is a sword that is imbued with gravity control magic, meaning it can fluctuate it's weight (density, I guess?) at the turn of a dial on the handle.
I think something about Negima that I don't like as I look back is the time it took to figure out what kind of manga it was. It spent most of the first half of the story being a harem manga with some magic and shonen battle elements mixed in, then finally took the dive as a straight-up battle shonen scifi/fantasy mashup.
UQ Holder is also kind of taking it's time with that identity in some ways, but it's been made clear that this is a shonen battle style manga from the beginning, and it's not taking overly long (so far) to establish all the ground rules and players. Touta as an MC suffers from that pervasive MC vagueness that some anime have, with his dream being just 'achieve glory with friends' and finding ways to mix combat and battle into ingredients for that.