From my perspective, Facebook marketing is effective for markets that use Facebook for their information or entertainment needs. Where these two factors compel them to a purchase is the key to using the platform effectively. You need to know your target market well - the better you do, the better you will be able to reach them on Facebook.
PPC (Adwords / Bing) is directed to search engine traffic (content networks excluded) where the emphasis is on keyword generated searches. The appeal being your ads relationship to the solution being sought by the searcher.
I think that you just found a better way for "you" to find your target market. I would think that if you knew how to optimize for your market in SE PPC and if your market depended on the SERs for their solution base, you would find PPC on Google or Bing a much better ROI (this also depends on the price of your product).
I would, however, recommend Facebook for most novice advertisers who are starting with a PPC strategy and then rev up to Bing and then to Google.