There is good evidence now that Tyrannosaurus may have been directly descended from Daspletosaurus. A while ago, a specimen was found (MOR 590) that was a cross between T. rex and D. torosus, with no characteristics unique to itself. There are also specimens in New Mexico that are a possible new species. There is also a distinction between specimens from the Old Man Formation and the Dinosaur Provincial Park Formation specimens, so that makes two, three, or even four species of Daspletosaurus. Again, we wait for the studies to hear more.
Daspletosaurus was a large animal. It was not as big as Tyrannosaurus, but almost. It was a strikingly hefty animal, compared to its contemporary Gorgosaurus. Tyrannosaurids are very similar animals, but having seen a few Gorgosaurus specimens, the Daspletosaurus I saw was certainly distinct.
There are now about six good specimens of Daspletosaurus known (although parts of several others have been found). The Royal Tyrell has one mounted at their Field Museum in Dinosaur Provincial Park.
This is my picture of that specimen.
There is an excellent mount of Daspletosaurus at the Canadian Museum of Nature, that is well worth visiting.
Here is my picture of the Canadian Museum of Nature's skull.