EDIT: The following review is based on an older version of the game. It's at least tripled in size and content since then.
Slayers is a pen and paper rpg about monster-hunting in an infinite, self-generating city. It's also a heck of a good pick-up-and-play game, and basically perfect for one-shots or nights where a few folks don't show and you need a new game on the fly.
In length, it's 23 pages, with relatively bare layout and a little bit of art at the beginning that escalates to a lot of art by the end when you hit the monsters section.
Mechanically, however, Slayers is very solid throughout. It's a combat-driven game, with the PCs' ultimate purpose being to track down and eliminate a monster, and Slayers has a good crunch to it without getting too complicated. There's HP, but not massive amounts, and any damage feels significant. There's skills, but not a boatload, and each one feels relevant and useful. Rolls use a variety of dice, but always succeed on at least one 4+. Characters are Class-based, and there's only four Classes, but they feel *very* different and there's a lot of room for mechanical customization in each.
The setting isn't described in great detail, leaving it very open-ended, but there are a lot of GM tools, including a sample scenario, a bestiary, a GMing guide, and a single-page quick reference for the system rules.
Overall, I would strongly recommend Slayers to groups that want solid, game-y feeling mechanics in an otherwise lightweight system. And I'd recommend it especially to groups that like a focus on combat and gothic atmosphere.