This kind of blew my mind.
ICRPG is a pretty rules light game, so if you want tons of different rules for everything THIS IS NOT FOR YOU.
However rules light does not necessary mean mechanics light if that makes any sense to you.
Hankrin (or if you wanna be technical Brandish) has some really interesting design ideas but what stands out to me the most is the GM chapter.
If you're not interested in the system I'd still say get the book just for the GM stuff alone wich tbh is the main reason for me to buy RPG books in the first place: more GM Ideas. But where most RPGs come to the GM chapter and basicly just say hey you're a GM, go do GM-things, ICRPG actually gives you guidelines on how to GM.
Holy fly that GM chapter.
I dont think I've seen a GM chapter before that was that gave you that many mechanical ideas about how to make your game faster and more dramatic. (apart from maybe some PbtA stuff but those are usually more focused on giving you narrative tips)
The session-end roll might be the biggest wtf moment I had in a while. Also the chapters about story and encounter architecture are really refreshing. Remind's me a bit of Sly Flourish's Lazy Dungeonmaster but better explained. It's all about being fast, keeping the pressure on your game.
The chapter about Room design actually helped me finally understand how to make a room more interesting than just your ordinary "The room is 10 feet by 20 feet there is a goblin" (well ok I already knew how to make a room more interestign than that but hyperbole helps to bring the point across I hope) by actually categorizing rooms themselves as a kind of challenge.