The film was certainly a commercial and critical flop but I wouldn't go so far as to call it a stinker. It certainly has its own fans who view it as a cult classic. I wouldn't go that far either.
For me, "Unforgettable" was both frustrating and compelling in equal measure. The story was utterly preposterous and threw away any chance of being an effective whodunnit thriller, by an early revelation of what could have been a good plot twist. At the same time, however, Dahl still displayed the flair that was so evident in his earlier movies.
So I'm looking forward to viewing it again, primarily to see how I will feel about it now, after a gap of nearly 20 years since I last saw it.