I want to bring http://theyeshiva.net/ to the readers' atention. It is a good place to start for those who want an introduction to Chabad Chassidus on an intellectual level. It contains well organized presentations of key concepts in Chassidus, well arranged and well explained. mostly from LIkkutei Torah and Torah Oh but also from other classic Chabad works. It sticks closely to the published maamorim without the fluff.
Those who are not familiar with Chabad literature have little concept of its extent and rigor. Otzar Hachchma has an optional Chabad module for purchase - 7000.00 volumes. The Maamorim of various Rebbes are built on one another and interlace in various ways. presenting a profound, complex and self-referential approach to Kabbala in its Beshtian interpretation that I would put on par with, say, Ramchal's approach, except that it is a living tradition that is revered and studied by thousands in our own day (most of whom do not understand it or shrink from its potential implications). It is deeply paradoxical and properly understood is not for the faint of heart. This site is a good beginner's introduction to the actual maamorim, without undue emphasis on the complexity and paradoxes.
If you are interested davka in the paradoxes, consider these two books: by Levin and Wolfson. The former is clearly written; the latter will strain your mind to integrate disparate concepts and your ability to understand English sentences.