Ahh yes I somehow forgot about Legends. It's a pity we never got to see Sonia in 3D, and that her in-game graphics couldn't live up to her cutscene and manual/cover illustrations. I'd also like to add that I don't think the artwork in DoS and PoR are as bad as people say, or bad at all really. I do personally prefer Ayami Kojima's art and find it much more atmospheric as I suspect most here do.
But I don't think there's actually a lack of quality in the portrait/illustration art of DoS/PoR, comes down to taste etc. Of course the shift inbetween AoS and DoS is jarring and I think hurts the latter game since as one of the few direct sequels in the series* the sense of artistic continuity is more important than it normally would be.
*Depending of course on how you define "direct", I mean starring the same central characters within a short frame of time. And especially if the actual games themselves are made within a reasonably short time of each other like CV1/SQ CVA/BR RoB/SOTN