Notes on this, Samuel comes up from the ground to join Saul as a ghostly figure and basically tells him if God won't help you neither will I. So, are we to believe that this person who is not a prophet of God can summon spirits? Spirits are floating around under the ground? This is in fact a pretty rough clash of ancient and modern scientific understanding of the world.
Samuel is popping up from "Underworld." Realize, this is not the point of the story. It is an assumed fact around it.
The intrigue continues. David has pledged allegiance to a foreign king and it looks like he and his army may actually go against the Israelites under Saul's command. Although that doesn't happen because the Philistine generals, with whom this new king is buddies, are like, "Hey, we remember that dude. Uh, no, we're not going into battle with him." David executes a daring rescue of his family and the whole city which had been plundered by the Amalakites while he was off almost fighting against the Israelites. But, this book is really about Saul. And it ends with Saul's sad suicide the same day everyone of his boys dies in battle. (Cf. Eli, his sons and his daughter-in-law mother of Icabod).
Psalm 18 is a little braggy for my taste. It is full of how awesome God is, compare to the end of Job, but also a lot about how pure David is, I guess also compare to Job. But, it comes off differently when the speaker is a king.
Closing thought, Saul feel like Darth Vader to me. Much more interesting from a literary point of view than goody two shoes David (so far).