Although it uses Smalltalk-80 syntax (almost), syntax is the least important part of Smalltalk. The real juice is the idea of a computing environment small and beautiful enough for one person to understand entirely - and fun! Toward that end, we feel that Pharo is evolving far enough beyond St-80 that it's more useful to think about it on its own terms.
Unfortunately, ideas that are truly different than the status quo are impossible to describe in a sound bite. Like learning to play a musical instrument, there is no shortcut - extended play is the price one must pay to shift to a more powerful perspective. But I hope this gives you a taste. If you're interested, I go a bit more in depth [on my blog](http://seandenigris.com/blog/?p=1092)