Hostas are very nice shade loving plants and come in various sizes (from small to huge). Not all of them bloom but some are gorgeous!

How about Astilbe and Asiatic Lilies? You might shoot for a variety of perennials that bloom at different times and offer different textures to your hostas. Different bulbs would bloom at different times and you just plant once. What about a taller ornamental grass? Much of your home has a horizontal view. A vertical shot of color or texture would attract the eye. Have you considered hanging baskets with more color to add to the 'pop'? Too bad you're so far from the curb, but it's a beautiful home and a very serene view.

Can you take a photo of the planter from closer in? Is it against the foundation or freestanding? How tall is it? How wide is it side to side and front to back?

In zone 5 it is difficult to find perennials that can survive in an above ground planter. Without being surrounded by the mass of soil like in ground plantings, often the soil in a planter will freeze solid, and at both ends of the winter the repeating cycles of freezing and thawing is also difficult on plants. So the only plant that I have been successful in overwintering in an above-ground, free standing planter is ribbon grass, a plant that is too aggressive to be set free in a garden bed. I don’t think it has the mass needed to work in your planter. So you may be restricted to annuals for spring summer and fall, and arrangements of greens, cut branches, and lights or ornaments for winter interest.

Caladiums--lots of color and some height.