You're far from the only person who underestimated Paul as a singer without Art, Sooty. In Simon and Garfunkel, Paul usually would root the harmonies while Art would add the flair (look at "The Sound of Silence" for a great example of that). While he isn't the kind of singer who can do a variety of things with his voice but he has that delicacy and clarity that really understated. If you're looking to get into Paul's solo work most people would tell you to go with "Graceland" but I personally would recommend "Still Crazy After All These Years" (which "Silent Eyes" is the closer to) because it's my favorite. It has Paul's only #1 solo single on it in "50 Ways To Leave Your Lover" and you can find the final Simon & Garfunkel song, "My Little Town", on it and I think that familiarity could ease you into it a bit more.