Not having an iPhone, I only use Apple Pay on web, and there, it's very nice. It uses its own UI/UX during checkout for your personal/shipping/payment info, which is standardized, and almost always nicer than random retailers' websites, and doesn't give your credit card number to the retailer.
Yes! Just not having to type my address is a bonus.
In the UK it means I can do contactless payments in excess of £30. I now no longer carry a wallet or have to remember a PIN, and at the same time I have zero anxiety about security. I could live without it, but it's something I use every day and think is more or less perfectly formed.