The comedy in this show is amazing. So are the characters.
The setting/atmosphere of the first season is very good: A city of dungeon climbers, the quest, the competitive nature of the climbers and their co-operations. This works well with the main character's feelings and his relationship with his brother. Coopa is awesome!
Of course the anime has that flaw of believing in yourself to win battles but it doesn't dwell on it. Its actually more about others believing in the main character. It gives some appropriate consideration to the fact that minor characters die. Drags a little drama too long.
The second season gets continually more random and hard to get into.
"He will live forever as the sovereign of a vast nation.
Yes very." -dialogue
This is explained a little later on but i couldn't get into this part of the story. Fighting animation starts show only the weapons of the characters more and more. The little girls are creatively cute.