I haven't used it much myself, but I've watched a lot of Alan Kay videos and I've read his "Early History of Smalltalk" which I highly recommend. My take is tha

I haven't used it much myself, but I've watched a lot of Alan Kay videos and I've read his "Early History of Smalltalk" which I highly recommend. My take is that it is largely about creating a computing system from the smallest yet most fundamental/powerful building blocks. In smalltalk, "everything is an object", which means everything has the semantics of a "whole computer". These computers are networked together and can send/receive messages back and forth with each other. This creates a drastically different paradigm than simply creating a pipeline of functions to send data through (for example). It excels at modeling complex systems, it's really "OOP done right". Of course there are other interesting features worth talking about, such as "images" and the introspection capabilities. Which are both great and often sorely missed in todays systems. But I think the big idea is to try to understand what Kay had in mind with OOP. Another aspect of smalltalk that is important, beyond just the "language" is to recognize its role in advancing "personal computing". Smalltalk was essentially an operating system that empowered the user to create new media and tinker with the system. If you want to see a modern web-browser based smalltalk-like system that uses javascript, check out Dan Ingalls' Lively Web. That will give you an idea into how smalltalk systems were meant to be used, in terms of "personal computing".