PayPals API certainly isn't the worst but it's pretty awful. So much pain doing PayPal integrations. I assumed it just kind of happened but I'm shocked if you guys thought it was good... See Stripe for an example of not to abuse your API users.
It's not perfect but I'd like to point out that it was born in 2000 and still works fine today 13 years later. I think all the sample code I wrote is still in the PayPal docs somewhere.
The most painful PayPal integrations for me were the SOAP ones.
