There are way too many quirky things about this game to be touched upon in a single paragraph. So, I'd have to settle with 3.
Firstly; it is, in essence, a city-building game. You, the player, would need to assemble a group of 5 retired adventurers. It would be optimal to have different classes for each, which I will delve deeper into later. With their combined riches, you will be tasked with building a city and attracting adventurers with the same classes as your chosen characters. Not only is this important, there are unique buildings that each class could build and those would affect how you will beat the game or lose it.
Secondly; it is a resource-management game. You will need to learn the strengths of each class and exploit them as much as possible. Dwarves have a higher chance of building gold mines to strengthen your economy, halflings excel in feeding your populace, fighters give you cheap and plentiful housing, elves can make your city become a tourist resort while wizards and clerics will bolster your offensive and defensive capabilities against various enemies.
Thirdly; it is a real-time-strategy game. Imagine battles fought in Warcraft viewed from the side instead of a top-down perspective. Warriors slash, Thieves stab, Dwarves hack, Elves shoot, Wizards blast & etc. Each skirmish is a joy to behold and a raid on a monster den is extremely epic, especially with a high level army toppling a dragon nest.
This game is a totally different beast of its own. If I had to classify it under a genre, I would have to grudgingly say that it is a 4X game. Even then, I am using that term extremely liberally. When another game with the same name came out 8 years later, I was ecstatic. I thought it was a sequel or a reboot. And then I was totally let down by it.
Don't take my word for it. Buy it, try it, love it.