I'm playing the 360 version.
Performance is about what EgonOlson stated. Framerate in dungeons is about perfect, while outdoors it hits the 12-18 fps range if you're fighting some guy.
I think they turn up the effects all the way, and it looks awesome
. More than makes up for any slow performance. Also, I get both HDR and AA on mine
What I really love is the shimmery effect you see on all the cave/dungeon walls, and how it responds to the spells you cast. I remember one particular dungeon (near the beginning, under that ruined tower with the couple of skeletons in it) where you can fire spells down a misty hallway and it just looks incredible. Also I remember a zombie or two coming out of the mist and seeing nothing but a silhouette of the creature in the distance, which I thought looked really cool. Really there's just so much amazing stuff in the game it's hard to describe it with words. I also love the color ramp effect when I frost-touch someone and they turn all blueish.
Oh, and besides the graphics, the gameplay is sooo addicting and fun and varied (combat feels very solid, and you're appropriately dazed for a second when you get whacked really hard in the head), and the physics engine is completely amazing. Honestly, I could have fun for hours just summoning things in the mages guild and throwing various stuff around.
And, looking back at your posts, Xbox 360 version hasn't crashed as far as I've seen (but now that I've said it... probably will).
Ahh, I need to go play it again. Gotta get some work finished first though. :\