I din't purchased SoD, so i can't have a honest opinion, only say what i've heard about it.
But talking about video games adaptations, all iterations of underdark that i know are high level to epic level.
- NWN1 - HotU starts at lv 15. And you only goes down to the underdark on chapter 2.
- BG2 you only venture on underdark when you have the slayer form and has a six party member
- DDO menace of the underdark is a high level/epic level campaign.
But maybe i an wrong. IF one thing that i learned is that you can't judge Sween by his words. He said "missing obvious not work", "spell slots aren't intuitive" among other things and the gameplay that i saw seems great. I can only judge how underdar will gonna be when i see it Note that spell slots is not something which only D&D uses. FF 1 and Dark Souls 1/2 uses it too.