The G series also ad a "restore" feature where (after it knows it has warmed up) it will run color tests on itself and restore itself to factory preset color settings.
The E and G are .24mm aperture grille, the F are .22mm aperture grille (shaper image on screen).
I have a G500 (21") and am quite happy with it after using it a while. It replaced a 19" G series that my dad has now.
Two friends at work have E series 21"ers, and i have played games on them pretty extensively, and my G series has better color depth, though it could have more to do with video cards than the monitors (i have an ATI 8500, they have GF3 and GF2ultra). I have also used an F520, and it had noticably better sharpness than my G500, though color was about the same (it was driven by an ATI 9700).
To me, the G series is worth the extra $ over an E series from what i have seen.