Overall I would say that is true mostly because the music composition and fight scene animations. Even then if they fuck up an manga ---> anime storyline good CG ain't going to do much.
Kinda like to bring Hellsing as an example of this.
Hellsing OVA > Hellsing Manga > Hellsing series
Animation done right is supposed to ADD to the manga series. Have all the key good story elements but make it look beautiful in color and sound good. Hellsing original failed at that which made the manga superior.