Horrifyingly bad decisions with architecture - Bulldozer completely obliterated AMD's desktop market. Intel doesn't even look at AMD's opportunities when deciding on engineer salaries anymore.

They're trying to make a comeback with Zen, but one of the biggest issues with development is that you learn from the successes and failures of your previous product. If your previous product sucked, you're under an enormous amount of pressure to fix those problems before you even get started on your next generation. Otherwise, those problems will persist, and you'll get new problems as well.

They've stayed relevant in the GPU market, though.