[runjake]

It's subjective, but from my viewpoint, the message passing and it's relative simplicity and readability, compared to Swift.

I can completely see why people would think the opposite, though.

[kalleboo]

Message passing is neat, but every time I saw someone take advantage of its flexibility, it was a mess.

E.g. there was a Flickr API library that directly translated the message names into API calls. Very neat, but now a typo stops being a compiler error and becomes a failed API call.

Mostly it was used to bypass Apple's private API App Store restrictions by obfuscating message names in rot13 or something.