The plot, as mentioned above, is ever-thickening. You'll go from Lina fighting some scrawny bandits to Lina fighting a Demon Lord the size of Kansas. There are really two main story arcs in Slayers . While the first one is great fun, the second one is really just a rehash of the first one. I don't want to give away any spoilers, but you'll see what I mean when you watch the series.
Slayers is a twenty-six episode anime, and the pace moves along rather quickly.
You can guarantee Gourry will be dressed in drag in one of these filler episodes. The writers just love to torture the poor guy. The artwork is not exemplary, but it really fits the pseudo-medieval RPG feel of the series. I'll also note that the animation is really good, but not the best you'll ever see. It's pretty typical for an anime produced around this time.