What makes this particular find of a feathered dinosaur important is that it extends the known time period and geographic range of feathered dinosaurs. All previous records list feathered dinosaurs as living in Africa in the early Jurassic period. Now we know that they were also living in Asia, and were around all the way up to the early Cretaceous.
Finding this fossil also resolved the dispute over phylogeny. Tianyulong is closely related to Heterodontosaurus and Echinodon. (See figure 3 below.)
Source: Zheng, X.-T., You, H.-L., Xu, X. & Dong, Z.-M. An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature 458, 333–336 (2009).
Link to extra supplementary information with cool photographs: http://www.nature.com/nature/journal/v458/n7236/suppinfo/nature07856.html.