The first thing I recommend is that you do not tell them that you are angry and will never fly Delta again. That takes all the insentive out of any customer retention concepts they might have. Why give this guy anything? He's not coming back!

Yes, Delta, along with all other airlines, has some problems. The situation you describe is becoming more and more commonplace. Perhaps reminding them that they have taken all the slack out of their system, and they leave us frequent fliers stranded sometimes would get the message across better. There's nothing wrong with telling them, "that makes me want to look at other carriers that might be more reliable than Delta." They do need to be reminded that we have other choices.

Good luck whichever way you go.