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You picture of your Nova Zembla doesn't show any specific problem, just a general lack of vigor. The essentials for a healthy rhododendron include:

I. Variety: The rhododendron or azalea must be suitable for the climate where it is planted. Nova Zembla is a good variety that should do well, even in full sun.

II. Soil Drainage: Because the fine roots of azaleas and rhododendrons are easily blocked by fungi, excellent drainage is important. To test drainage, dig a hole 6 inches deep in the bed and fill it with water. If the water has not drained from the hole in four hours, install drainage tile to carry away excess water, or build raised beds. Moist well-drained soil is a must for most varieties. This sounds difficult, but it means to not let the soil dry out completely but don't get it too wet. Thoroughly water if necessary and then let it become almost dry. Most gardeners do this by planting in a well-drained area and mulching to hold the soil moisture in. Watering is seldom necessary except during long dry periods.

III. Acid Soil: Most varieties require an acidic soil (pH 4.5-6). Powdered sulfur is the best agent to acidify the soil. Holly-tone has this in it. Your plants will get chlorotic if the soil is not acidic enough.

IV. Fertilizing: When rhododendrons and azaleas are not planted in ideal locations they may develop chlorosis. Chlorosis is yellowing of a leaf between dark green veins. Your Nova Zembla doesn't show any symptoms of chlorosis.

V. Shade: Some shade; some varieties like full sun to bloom but others suffer from too much sun. Nova Zembla can take full sun where I live in Pennsylvania. Prune off lower branches of shade trees so that you have "high shade" above your rhododendrons. This is ideal for a healthy rhododendron bed.

VI. Mulching: Rhododendrons do best when they have about a 2" to 3" layer of mulch to hold in moisture, prevent weeds, and keep the roots cool. Since most mulches are organic, they need to be topped off periodically, usually about every year or two. Do not make the mulch over 3" thick. Keep the mulch about 2" to 3" back from the trunk/stem of the plants to avoid bark split and rodent damage. Do not use peat moss as a mulch. It is a soil amendment to be used when preparing the soil in a bed and can cause severe problems when used as a mulch including dehydrating the soil and preventing moisture from reaching the soil. It also tends to blow around. It is best to mulch with a 2-inch layer of an airy organic material such as wood chips, ground bark, pine needles, pine bark or rotted oak leaves. A year-round mulch will also provide natural nutrients and will help keep the soil cool and moist. Rhododendrons have shallow roots and do not compete well with weeds and grass. Also, don't try to cultivate around their roots, this will harm the roots. Only mulch will keep the weeds and grass under control.

VII. Protection: In choosing a location to plant rhododendrons and azaleas, protection is very important. Protect from winter winds. This is especially true when the ground is frozen. Also protect from deer. This doesn't appear to be your problem.

VIII. Cultural Problems: Most problems are cultural. Cultivating rhododendrons and azaleas must be avoided. They have shallow roots and the roots will be severely damaged by cultivating. Weed killer from weed & feed products is a definite problem also. Salt from sidewalks in the winter is a killer to azaleas. Soil near masonry such as foundations and walks is usually alkaline (not acidic) and a problem. Lawn fertilizer in the fall can set an azalea way back. Another problem is the roots of walnut trees. They emit a chemical that is toxic to rhododendrons, azaleas and many other kinds of plants.

Here is a link that might be useful: How to grow rhododendrons and azaleas.

Thanks rhodyman...compared to previous years its taken quite a step back in flower production, and its kind of leggy, which my picture doesn't show too well. I think I need to raise the soil level into a mound around there and replant. I like the spot its in, but the gutter doesn't run too far away from it, so drainage might be an issue.