When Japanese office worker Azusa Aizawa keels over when she overworked, she is reincarnated as an immortal witch in a fantasy world. She would get by killing slimes and gradually build up her powers alongside giving out medicine to the neighboring village. Soon, she meets a more characters such as Laika, a red dragon who can take a human form; her daughters Shalsha and Falfa who were both made from the consciousness of all the slimes she killed for 300 years; Halkara, a competent businesswoman elf - yet at the same time a drunkard and a ditz who often is the center of abuse; Rosalie, a ghost girl, etc.
I've Been Killing Slimes For 300 Years and Maxed Out My Level is more or less a breather series. It is episodic without much in the way for actual conflict, or if there are some issues, they are quickly solved towards the end of the episode. Not to say that is a bad thing as it does coincide with the main theme of the show being a critique of Japan's overwork culture. But at the same time, because of this, it does sometimes leave more to be desired. Essentially, you could easily tune into a random episode of the show and not miss much.
Animation is nice for the show that it tries to be. There are some moments that are amazing to look at such as when Azusa and her family arrive to the demon world. No issues on the characters either. Practically every character is likable and has an interesting quirk to their personalities.