I find this preview a huge disappointment. I mean, it'd be pretty lackluster regardless, but the fact it's duergar is just icing on the cake... sad truth is, whilst TSR struck gold with the Drow, the Duergar never have been as good.
I mean, not only does their entire characterization and culture boil down to "they act like any other grumpy dwarven jerk, but unlike surface dwarves, there's no heart of gold under that cranky arrogant workaholic exterior", but they aren't even that unique: they used to share the Underdark Dwarf niche with a non-evil dwarf subrace up until 4th edition! Even drow have something more to them than just "Generic Jerky/Evil Elf" as an underlying culture...