This is the first in Applegate's 12-book 'Everworld' series, and I might not have read it if I'd realised that it ends on a cliffhanger and that the second book (previewed at the end of The Search for Senna) picks up the plot without a break.
Everworld is a world created by a coalition of gods: a world populated not only by those gods (mostly at war with one another) but by their followers and believers. A group of teenagers from contemporary America -- David, April, Jalil, Christopher -- are pulled into Everworld in search of Senna, April's half-sister, whose powers of witchery are blossoming. David has a crush on Senna, and wants to believe well of her. Which is why he and his friends end up on a Viking longship, off to battle the Aztecs and their bloodthirsty deities.
The social dynamic of the group rings true: gossip, friendship, awkwardness, humour. And the prose is sharp and snappy, with short chapters, excellent pacing and an impressive immediacy. Very readable, and I can see how it'd hook reluctant YA readers. I'm not hooked enough, myself, to read the other books immediately -- but I'll certainly read them.