The little improvements make this a big improvement over the 5d - both in image quality and ergonomics. Canon did some homework - the increase to 21MP and Video mode get the headlines, but it is the other stuff I think that make this a winner.
The new 3" LCD, quick menu (accessible from the LCD screen), dedicated AF button, 3 custom registers, Live view, Image quality, a/f adjustments, programmable menu, dust clean, better viewfinder, af-on button, weather sealing, etc . . . make a big difference. (Although I have not had the camera long enough to see if sensor cleaning works).
Live view is a major feature for tripod shooting. The 10x mode really nails critical focus, and focus can be checked anywhere on the screen. Remote shooting with live view is worth checking out and great for studio still life work or lens testing.
Without rigorous testing, the 5dII seems to focus better in low light. Using a 85L in situations the 5d hunted - the 5dII got it right. A quick test with other lenses confirm the 5dII will focus when the 5d cannot.
IQ at the pixel level compares to the 5d - BUT 21MP is more demanding on lens quality and shooting technique if you are going to compare 100% crops between the two cameras. (But that is like comparing a 16x20 and 12x18 from different cameras)
The new batteries are advertised at 30% more capacity -- but have a 100% price increase. My 5d grip and battery spares will cost 500 to replace for the 5dII.
Wireless grip WFT-E4A looks useful - not sure how the $950 price is justified considering wi-fi SD cards are less than $100. I have given it a 9 on price due to cost increase of accessories.
Auto-ISO is a new feature - but not available in M mode - and that is when I would want it most (To lock down aperture and shutter speed and have the camera select ISO).
AND for the bad news - the dreaded black dots. I've posted a half-dozen sample shots and hundreds are available on the forums.
I was quoted on C-net and other sights with solving the problem - but turning HTP off seems to help in only some circumstances. Shooting at ISO 50 for night shots shows the biggest improvement - hopefully Canon will provide a solution soon.
My usability complaint is the front and back dials are not programmable. I switch between Av and Manual, and the shutter/aperture controls switch.