We can be sure it won't be worst than the previous games.
Basically I'm sure it'll be pretty good...
I'd imagine so, regardless of all the "focus on gameplay, not graphics" stuff, Bethesda is definately not going to make a sequel with worse graphics than the last game, if you'll note, that's pretty uncommon in video games, unless for some reason the sequel was released on a platform with lesser graphical capabilities. And if Bethesda did, you can bet it would receive instant criticism. No, we can surely expect the graphics in the next game to be better then Oblivion, how much better, we can't say, but Bethesda will certainly make it better.
I'd rather they focus upon animations. I've played games with less than stellar graphics, but the animation was so fluid that I was so fully into the game that I could not care less how it looked. Fluid animation is what makes Half Life 2 still look so amazing (apart from the fact that it also has amazing graphics).
Bethesda definately needs to improve animations, as nice as Oblivion looked in screenshots, the lack of good animations did cause it's visual appeal when seen in motion to suffer, and no matter how many graphics mods you install in Morrowind, the animations are still atrocious, animations are an important part of graphics, because the game will be played in motion, and no matter how good your characters' faces look, if their movements look unnatural, it's not going to look right.