I'll jump in, largely as I haven't posted on GCA in months!
Northumberland is good -- not great. But for $40 it is hard to find a better value in the country. This is part Geoff Cornish and Bill Robinson, as well as some holes by Stanley Thompson associate Robbie Robinson, if I recall correctly.
The course starts on the other side of a road, and there's one hole played there before it heads to the ocean. If I recall correctly, there five holes on the ocean side, including a nifty little par three that plays alongside the water (with a strange boat resting behind the green). The remaining holes play back on the other side of the road, utilizing some interesting pines and a piece of land that slopes from the high side on the south to towards the ocean.
I've only played it once, but I'd played Fox Harb'r in the AM (a Graham Cooke course designed for Ron Joyce, the co-founder of the Tim Hortons donut chain and a fellow with whom I wrote a book) and then Northumberland in the PM. Fox Harb'r has a green fee of $250, and for $200 less, I'd argue Northumberland is a much more intriguing experience. Is it great? No. Is it worth a trip if you're in the PEI/Cape Breton area? I'd say so.
Other potential nominees include: Twin Rivers in Newfoundland (Carrick and Robinson), Waskesiu in Saskatchewan, The Elks Club in Calgary, Tarandowah near London, Ont. (a newish Martin Hawtree), Crimson Ridge in Sault Ste. Marie, Ont. and Timber Ridge near Brighton, Ont. I'm sure there are others who can chime in with their suggestions. These are all inexpensive, well designed and smart courses. We could use more like them.