PBase

Wonder why my EOS Canon 20D never seems to be in focus as crisp as my other older Nikons (F2a). Is it the focusing screen or something else?

Most likely your camera has a back focus or front focus issue

Before I suspected front or back focus problems I'd look into a few other things. Is it with all lenses? Are you shooting jpg or RAW? Either way, unless you're shooting jpg and have sharpening turned up high images from digital cameras should always be sharpened in software after downloading. What shutter speeds are you shooting at? What ISO? What lenses are you using? Digital is more demanding on lenses than film was. There are a whole bunch of factors that effect sharpness and focus. How you view the images also matters. Are you comparing 4x6 prints you did on film to images displayed full screen on a 24 inch monitor? Is it a high resolution monitor? So much to consider.