As the other ones in this thread have mentionned, YC is what you make out of it. For the fundraising alone, it allowed me to raise - a non US solo founder - at very comfortable terms and on the financial aspect alone it would have been worth it. But most importantly, the hardest part to start a company in my opinion is to keep being motivated.
I was under the impression that surely a successful startup wouldn't have to go to any struggle and that founders were a special - genius-like - kind of breed. Being in YC opened my eyes:
- everyone struggle, relax and keep working
- the great people of this world are smart, but not crazy smart. They are crazy pragmatic, and crazy motivated, which you can be TOO
- YC founders are nice people, and they make for great friends to keep. Those people are the only one that will understand truly what you're going through.
YC was a transformational experience for me and I would recommend it to all.
EDIT: To give a more balanced view, YC was also stressful, and the expectations were the same, solo founder or not. Be prepared for an intense ride.