The few detractors I found with the 3D visuals had to with the overall quality of the images on-screen. Since images need to be rendered twice when you have 3D turned on (you can turn it on or off at any time during gameplay) the developers at Treyarch had to scale the visuals back a bit in terms of overall quality. Thankfully the framerate was always sturdy despite the almost constant frenetic action. The other downside to the 3D capability was that some background images seem to distort to looking like the screen sans glasses (despite them being firmly affixed to my face), but that will hopefully be remedied by the time Call of Duty: Black Ops hits shelves.
Important bit from article.