I might keep this one a bit brief, because I'm re-treading old ground here. Having recently watched the Reincarnated as a Slime anime, I decided to hunt down the light novel and see how they compare.
Perhaps unsurprisingly, they're very similar.
Once again, the middle-aged salaryman is reborn as the slime Rimiru, encounters a dragon, escapes his cave and begins to explore the world around him. This involves goblins, dwarves, big dogs and a fair bit of fighting. It's still light-hearted in tone, with a comedic bent to all of the slime's adventures, and no significant horror to be had.
However, there is a bit of shifting around of the plot, with the introduction early on of some background regarding both the Hero (but which one?) and a character called Shizu, who was summoned by a demon. The story fleshes out her tale rather more heavily, much earlier than the anime, and this was a nice bit of additional info. There's some good story telling in that bit, which has a surprising crossover with the recent Hullmetal Girls regarding mind control.
In terms of extras, there's also a bit more about Gobta, the goblin guide, and the illustrations are unexpectedly impressive. There's a style usually used for the pictures in light novels, but this one goes a bit above and beyond in terms of detail and skill. (Now admittedly, I've got absolutely no artistic abilities, so I'm impressed by the most childish scribblings, or things by Damien Hirst, but these were pretty good anyway.)
If you're a fan of the anime, it might be worth you giving it a try, but simultaneously, you may also find it repetitive. Difficult to gauge. Still, there's about four books out at this point, so you can always read ahead. Handy if the anime never gets a second series, or progresses slowly.