Popular payment processor, used by many merchants. Thus, it's very convenient to make transactions with Paypal although fees are little high.
Unfortunately, it has restrictions in some countries.
The thing I dislike them the most is the security. Once they selected by the security team and forced me to change my Paypal password just because I logged in through many different IP addresses otherwise I permanently lost access to the account. They told me that this is to prevent fraud.
However, it's very inconvenient because I can only change to the strong and never used before password. Usually strong passwords indeed prevent hacks, but also prevent the user from logging in too because it's difficult to remember.
I know that I may save the password to somewhere else so I can copy and paste whenever I login, but that's also very inconvenient and dangerous because if I lost or someone saw it, then again unauthorised access will happen.