There are dozens, perhaps hundreds, of posts on this blog about Chabad, everything from the actual history of the movement (as opposed to the official Chabad spin), to Chabad theology. These posts are heavy on controversy and are not meant to present a complete picture of the movement. The aim is to call attention to the problems with Chabad theology and corporate behavior that negatively effect those of us outside Chabad.
Most of these posts are indexed here.
Posts specifically about Chabad history are usually found here.
Posts on Chabad's virulent anti-Zionism, which was the official position of the 5th and 6th Lubavitch rebbes, are indexed here.
But it is Chabad's messianism that is the most disturbing and problematic feature of the movement.
To understand what Chabad messianists believe, listen to this debate between Rabbi Irving "Yitz" Greenberg, formerly of CLAL, and Chabad messianist Rabbi Sholom Ber Kalmanson. The debate is posted as three separate mp3 files. The second and third are the most interesting. I point out the factual errors made by both rabbis here. (Especially note Rabbi Kalmanson's misquote of the Rambam.)
Then we have an article by Rabbi Shmuley Boteach and a rebuttal by Rabbi David Berger. A Chabad messianist writes to 'prove' both Rabbi Boteach and Rabbi Berger wrong.
Posts noting parallels between Chabad messianism and Early Christianity are indexed here.