He basically was Mizuki-sensei but with better looks. One thing to be wary about UQ Holder is that, despite having a lot of ideas that technically should make it different, it's still very derivative of every other action *and* harem shounen out there.
Touta never gets angsty about the immortality itself (it helps he's not that attached to anyone he would outlive, and all his best buds later on will be immortals as well) but there comes a point where he hits a major angst spike because of something else, be warned. Overall he's a likable enough guy, but his motivations are mostly lacking most of the time, and he's the kind of character who really would work better as a support player. The plot suffers a lot from having to spin around him (and then around Negi's shadow) constantly, since eventually it feels like the other characters, except for one or two, matter very little at all.