That Time I Got Reincarnated As A Slime is a fairly unique take on a “trapped in a game” story. After a 30-something year old man is killed, he wakes up in a fantasy world. As a slime monster, traditionally one of the weakest enemies in fantasy video games. From the start, the storytelling features a sense of humor as his last, dying thoughts determine what abilities he starts out with as a slime. Which are crazy overpowered, by the way. Throughout the story, many enemies underestimate him due to his race. But stories with OP main characters can work so long as other narrative elements are done well.
While protagonist Rimuru is powerful, this is an alien world to him. He does not understand things that even weak monsters consider common knowledge or basic instinct. Because of his power, a lot of other characters just assume he knows these things as he stumbles into them. As powerful as he is, Rimuru is very much a fish out of water here. But that ends up being as much of a boon as a curse. Since he was originally human, Rimuru thinks differently than most monsters. His creative solutions form the basis for future plot elements.
Compared to other “trapped in a game” stories like Sword Art Online, this series is fairly light-hearted. There are dark moments, but the author uses humor to balance them out. In one way, this series is like Log Horizon in that there is no going back. You are just in a game world now; deal with it. But it is also a bit like Overlord in that the protagonist came to this new world alone. “Trapped in a game” stories are a hot topic for light novels, and it is good to see different authors take slightly different approaches to the subject.
A friend introduced me to the TV adaption of this series before I read the books. The first eight episodes of the show cover the events of Volume 1. Some scenes were reordered or skimmed over, but it did not affect the overall story too much. This is less true for the later volumes. The show currently covers the first four books, but things got rushed at the end. Some parts of the story were skimmed over or left out entirely to save time. If you really want to get into this series, read the books first and use the anime as supplementary material.