First things first: "Eric" is the shortest Discworld novel to date. Even printed in a larger type face, it's slim on the bookshelf placed next to the rest of the series.
What that means is that Pratchett didn't provide this novel with multiple interwoven plots, there isn't the female friend/companion who turns into a love interest (a staple of his novels) and all of the action is very narrowly focused on failed wizard Rincewind's escape from the Dungeon Dimensions, where he was trapped at the end of "Sourcery."
He gets out when Eric, Discworld's would-be Doctor Faustus, a spoiled brat turned amateur demonologist, summons a demon from Hell and gets ... well, him. Somehow, Rincewind has been gifted with the power to grant Eric's rather venal wishes. These take the duo (trailed by Rincewind's sentient and extremely dangerous Luggage) through time and space. Along the way, we get parodies of Aztec religion and Ponce de Leon, a particularly well-done riff on the Trojan War (superior in every way to the quicker one in "Pyramids"), visit the beginning and end of the universe and see what Hell is really like.
Without the need to slow down for a B-story, Pratchett moves through the story at a rapid clip, making this one of the best Rincewind tales to date, as well as tying up a loose end. (Pratchett has a bad habit of doing that with Rincewind; the first Discworld novel ended with him falling off the edge of the planet.)
Know that you're getting what amounts to a novella in a novel's packaging, but otherwise, "Eric" lives up to the high standards Pratchett has set with his previous works.
Recommended to fans of Discworld and Pratchett's collaboration with Neil Gaiman, "Good Omens."