The graphics have unsurprisingly made leaps and bounds over Ultima Underworld (it was made at a time when any 3D was a novelty), but you might be most interested in the variety. The usual grim dungeons and dark caverns are broken up by underground flora and other signs of the not-so-natural life in the Stygian Abyss.
The teaser still leaves questions unanswered. Does it translate some of the clever role-playing elements (such as learning another species’ language), for example? And how much will it feel like an Ultima game for those who remember the series when it was fresh? Ascendant is still slated to ship in 2018, so you might not have too long to wait to get further answers.