Their flowers are great, big and long lasting in late winter or very early spring when even a little bloom goes a long way. However, hellebores are good for so much more than flower!
(To jump to the article and downloadable chart that also includes this plant: Easiest Best Perennials.)
They have distinct form -- no matter the season, they're a reliable mound about 12" tall and up to twice that wide. Even in dim light the mounds are notable when surrounded by vertical or mat form plants.
They have coarse texture. Their leaves are large, so their edges and shadows create a bold pattern of light and dark on the plant surface. Coarse plants stand out near fine plants like bold polka dot print cloth stands out from tweed.
Here they are in bloom at the base of the "tree" trellis, and again throughout the season contributing by way of their coarse, dark foliage. They provide contrast and separation between the fine textures of arborvitae hedge behind and boxwood in front.