United is a mess. I had the misfortune of flying with them a couple months ago. I ended up in a city a 2 hour drive from my actual destination and had to rent a car on my own to get to where I was going. That was the worst of it, but almost every flight I saw on the way (both ones I was on and other flights at nearby gates) was delayed or overbooked or otherwise messed up in some way.
If I ever listened to horror stories like these, there wouldn't be an airline left I would fly with. This is textbook; replace United with Delta, Southwest, Air Canada, etc., at will. The only company I've used that I haven't heard exactly this type of complaint about is Widerøe, a tiny regional line in Norway with a fleet of prop planes. This is unfortunate, as I live in Pennsylvania and get motion sickness on those…
Obviously, with travel sometimes things go wrong, but the quantity and severity of things going wrong at United makes me think there's something off about the way they're running their airline. For instance, the two times this year that they've had to ground all flights.