i had exactly the same with upgrading to my 5dMk2.
plastic fantastic body
simply bad image quality compared to whatever digital back at low iso
bad autofocus
very easy to get "moving blurred" images because of bad body construction
miles away from the built of real body such as 1DsMk2/3/1
bad balance when using pro lenses etc....
but still it is the most bought camera among pro's.
shot yesterday with 5dmk2 in left copper mine.
two hours walk inside the earth together with my assistant till we met this dead monster..
90-100% hum, app 30 degree temp,
800iso. 30 sec exp. 24-105 canon L lens ( a selected one ).
smallest gitzo carbon ( 200gr? ),
2 canon 420ex flashes with several exposures.
i recommend to repeat a shot as this with mf equipment with or without "+" technology.
[attachment=12528:090326_1...k2_small.jpg]
100% crop of image
[attachment=12529:090326_1...mk2_crop.jpg]