Adding Smalltalk message passing as an extension to C was very clever and allowed writing very efficient code and dynamic high level UI code in a single language. The semantics were kept clear by the distinctive syntax of message passing. And allowed access to any existing C libraries.

Objective C is neat inasmuch as it managed to add a simple but practical object system to C without all the added baggage of C++. It wasn't without its downsides - in particular, the overhead of a method call was significantly higher than in C++ - but I still appreciate it for its minimalism.