Adobe's fonts are designed to look the best on EGA or VGA monitors. The
change in aspect ratio of a large screen monitor may make a difference in
the way the fonts view on screen. It may be that the video card is unable
to calculate exactly at certain point sizes or page views, thus the "heavy
condensed" appearance. Fortunately your fonts are printing fine and the
metric files (PFM) should ensure that the spacing etc. is accurate from
screen to printed page, even if the fonts do not look as pretty on the
screen.