I played it only on Dreamcast, american S1 and euro S2, and heard a bit of other versions on yt.
I know Ryo as a bit stoic, sometimes he shows his emotions, but not all the time. I felt that some acting could be better, specially Nozomi -and Ryo too, specially when talking to her - , since she loves him too much. I know that she must sound shy and all, but the english voice is even milder than the japanese one!
So, for S1, the english voice acting IMO only adds in experience and emotion, not being a masterpiece but not half bad too, and miles ahead any other games at the time.
As for S2... I never played it dubbed in english, but it seems that the actors had only sparse phrases and some emotional accent note, but no actual scene seeing, so my impression in the videos is that almost all dialogues are very artificial.
I will watch this interview, seems interesting.