Why is iMessage all the rage

I am an Apple user. I have iPhone, macbook and desktop mac.

I see that people make a big fuss about iMessage. I don't think it's all that great. That's not saying i think it sucks, but i'm unaware of any advantages i am receiving by using iMessage as opposed to messaging apps on different platforms. Am i missing out? Am i not using it to it's full capability?

thanks