It's slighly above average for an idle game,since it gives you an objective(conquer the overworld) and the flavo text is rewarding since it's simple and fun.
However,the game is lacking in certain fields,namely the selection screen before attacking the overworld.there should be a max option so you don't have to manually add them one by one(the 10,25 and 100 are seldom used since you need to have at least this value to use once)