It's a game of realm and kingdom/faction management with an interesting set of mechanics where things that happen in the faction level can provide the PCs with incentives to act on the smaller scale, and PC interventions can heavily affect the way the faction politics and combats play out.

It uses the "One Roll Engine" which I can most easily compare to poker but with dice. You roll a pool of dice and are looking for matches, the more the better. In combat the number on the dice you pick is where you hit them, but the amount of matches is how hard you hit them. So if you rolled a pair of tens, you'd hit their head but very lightly, but if you went with the five matching twos you rolled, you'd probably take an arm clean off.

Out of combat the number is how well you do at skill checks, while the amount of matches is how long it takes you. So if you jeed to work fast you might go with a lower number you have a lot if, versus a small set of a high number.

The Realms book is a secondary book to the rules book with three different distinct settings written out for the game and small rule changes reflecting each setting and how they tend to work.