It's funny to consider, but Robert Baratheon was the most successful king. He was complacent, and let the schemers have a lot of influence, but, he did what was necessary to keep the kingdom together. He built his alliance with the Lannisters whenever it was needed. He's swiftly addressed the Greyjoy rebellion.
The lack of attention caught up to him, but, it says something that people waited until he's died before they attempted the more blatant power grabs.
Now, when your best leader is a fat drunk who's burying the kingdom in debt, it doesn't bode well.