I'm tending towards optimism when it comes to Skyrim, so I think the new engine will be a major factor in giving us a superior game.
Look at these two youtube clips and see if you can manage to tell me that keeping crappy Gamebryo would be a good thing:
http://www.youtube.com/watch?v=1Kvl31g77Z8
http://www.youtube.com/watch?v=-D9oINHI11E
CryEngine 3 looks extremely cool; if Bethesda's can do half of what is showcased there we'll have plenty to be excited about. And while I play on PC exclusively, it's nice to see that spectacular things can be run on the consoles as well (ie, they needn't be excluded due to console releases).
In particular, did you notice CryEngine 3's colour grading and blend shading? With that kind of power over the environment, the frequently hoped-for changing seasons would be a real possibility. But yeah, I'm being optimistic. Roll on January's screenshots & info.