There were twelve arcs. The first started in December 2000...Fate. It focused on Ian and Eve's love story, and Kevin and Lucy getting back together. Following that was the first supernatural arc...Time In A Bottle. That was Karen and Frank's love story. Tainted Love was third...the introduction of Caleb, the vampire. Tempted (which aired around the time of 9/11) mixed up all the characters and introduced Rafe, Lucy's cousin/angel. It also marked the exit for Caleb, for a time. Miracles Happen was the shortest arc...lasting only one month. Lucy and Kevin got married, Julie (one of the interns from the early days) made her final appearances. Secrets started in Jan. 2002. It marked the ending of Jamali and introduced Rali, and brought in three angels who caused problems for the citizens of Port Charles. At the end of that arc, the angels all went back to heaven (including Rafe and Eve, the Fifth Chair). Superstition is a little hard for me to define. It was a mixed bag of witchcraft with Alison and Livvie (who had found a memory-less Rafe after he made a deal with the devil to return to earth) primarily the focus. Torn was a lot of the same, but at least Rafe knew Alison existed even if he didn't remember her until the end. Livvie shot Rafe and sent him back home, but he returned again...this time as human (or so it appeared). Naked Eyes focused on the reuniting of Rali and the return of Caleb as Steven Clay, a rock singer, with Jack finding Tess, Livvie's double. Surrender involved everyone finding out Caleb was back...and what they did (independently and together) to stop him. Ian became a vampire. Caleb didn't seem as big a problem as his so-called manager, Joshua, who'd become a vampire and decided to get rid of the slayers and others. At the end of Surrender, there was an explosion with several characters in jeopardy. Desire featured Joshua's decision to marry Alison by brainwashing her, while Caleb was suddenly human...but with his own problems...Livvie was now a vampire. Caleb and Rafe teamed up to get rid of Joshua. Karen died and Caleb became a vampire again as the show went into The Gift, the final arc. Unfortunately, at that time, several of the cast...Amanda Barrington, Frank, Kevin's father, Jamal...had joined Ian as vampires.
I loved the arcs, and I'm a Rali fan as well as fan of Caleb with Livvie. I really miss it.