The love for Ripples is easy. It's a sad, beautiful song about something which we all must face, and which we all fear, so it resonates with everyone. And the instrumental section is mesmerizing.
I'm with you on Robbery, Assault and Battery, though. That one kicks ass. The "chase scene" in 13/8 is amazing.
Every song on A Trick of the Tail kicks ass. Genesis knew that they had to nail this one, their first without Peter, and I think they hit it out of the park. The weakest song is probably the title track, and even that one has some intricacies and complexities that aren't apparent until you try to learn the song. That's a tricky song right there, and it's the easiest one on the whole album.