Starting with the obvious, Bethesda's Starfield is going to extend beyond the stars and explore a brand new universe - which is an incredibly exciting prospect. Bethesda's big flagship titles have always had the same overarching design, and transferring the ideology behind Elder Scrolls and Fallout into space simply opens up a whole new realm of possibilities.
It is also perhaps the single most creative decision Bethesda could have gone for. It would be unfair to say that Fallout and Elder Scrolls have been stagnating, but it is incredibly interesting to put the creative minds behind those games into a genre that is known for its creativity. The combination of a sci-fi space opera and Bethesda is a recipe for sheer brilliance.
As for the style of space game they are going for, that remains to be seen. However, the brief teaser they provided us seems to edge towards a more realistic approach. The space-station shown in the teaser is hardly wild sci-fi and bears a slight resemblance to the real-life international space-station. It appears to draw more from tangible rocket science as opposed to Star Trek's technobabble.