No one was more active in bringing Jews back to Torah umitzvot than he, and no one is more aggressive in bringing Torah umitzvot to Jews. Whether it's Katmandu, high in the Peruvian Andes, wherever, if there are Jews you'll find Habad. All too often it's the only game in town. While nobody is infallible, and the Rebbe was flat-out wrong about evolution and Ethiopian Jews (whom he didn't consider Jews despite the Israeli Rabbanut's ruling to the contrary), we are immeasurably richer for his having been with us.
Toward the end of his life and even more so after his death, his good work has been shadowed by a Messianic current. It is not rare among Hasidim to tout their Rebbe as a potential Mashiach; until now the touting always ended when the Rebbe died. Perhaps because the Rebbe's work was so successful, the Messianic rumblings in Lubavitch got totally out of control. While he was alive and well, the Rebbe did not encourage this kind of thinking, telling his followers to just go out and do mitzvot and never mind who Mashiach is or might be. Toward the end of the Rebbe's life, when he was too weak to object, the rumbling got louder and louder. Children were taught to recite: Long live our master, teacher and Rebbe, King Mashiach, for ever and ever. After he died many hasidim seemingly did not accept the fact that he was dead. Children are still (after 12 years!) being taught to recite the mantra, and posters appear referring to the Rebbe shlita - an honorific applied only to living persons. These Messianists, centered in Crown Heights, where the movement's headquarters ("770") is located, think nothing of muddling the distinction between Judaism and Christianity by propagating the possibility that Mashiach could die with his mission unfulfilled, then come back to fulfill it.
Fortunately, the shluhim on college campuses, for the most part, are either not Messianists or keep their Messianism muted, knowing that that is not the way to attract students or raise funds. One can only hope that cooler heads withing Habad will regain control of the movement, possibly appointing a new Rebbe, so that Habad can continue its holy work without a dark cloud hanging over it.