Sound: I still remember the opening songs, all beautifull music
Animation: Animation is top notch, fighting scenes are well animated
Characters: Although one might say this is the most standard anime, it succeeds in just that, humoring, weirdos, joyfull people, childs, serious people mixed in with eachother for a good blend of personalities.
SMALL SPOILERS AS A SUMMARY OF STORY HERE
Slime meet tsundere and gets OP
Helps a goblin village
Saves gobling village 2 times
Saves some people
Defeats demon lord and gets stronger
Defeats calamity too fast for comfort
Goes really far away to educate 5 children
Helps those 5 children through a labyrinth to save them
The first 6 points are all connected, but the last 2 are just a random filler arc in my opinion.
He practicly build up a whole nation, but goes to another nation's school to teach 5 children because of a promise made to someone dear to him.
Although i get it, it doesn't really add up. If this arc was brought in sooner i might have enjoyed it more (even though it wouldn't line up with the light novels then), but with him ruling over the whole Jura Tempest Federation, it doesn't make sense to me for him to go to that city.
Overall i really liked the anime