Beat story at lvl 50(coz did a bit of sidequests ;P), even finished that hard af dungeon that lets u change difficulty to torment, so far 0 forced p2w mechanics, all those mtx costumes are purely cosmetics, that no1 sane cares about, will let u guys know if something changes but so far its solid singleplayer experience, hack and slash with good story/fun gameplay.
If u play on lowest difficulty story alone w/o any side missions is easily 20h, if u go to normal(called veteran here, i recommend it if u are diablo series fan or/and experienced player who is capable of learning bossmechanics) then its around 30h.
Im ur neighbourhood GAAS shit/always online hater but even as one, i tell u at least for now i enjoy d4 a lot, ofc we cant be sure in the future if and how many p2w mechanics blizz gonna introduce, so can just tell u how it looks for now- solid 0 gaas singple player fun experience.