If you're comparing the full Diablo 2 game to a short BD demo => you're comparing apples with pears => I suggest a fruitsalad, makes more sense <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />
Kiya
As Bronthion and Fredric /Larian Studios were in charge of quests, I'm sure, there will be more than simple quests and not only hack'n slash.
As you get summoning dolls later on, you will have more party members to control.
I'm sorry, there are definitely more than 10 skills. Please open the skill tree (left lower icon in skill table) and look at Shaman Magic (nature or weather part) eg. - look at the path cursing - look at the converting arrow part - have you seen how large the variety of traps are? Etc.
Kiya