It might not pay off immediately, but it could, eventually.Trading at a bit under $25 apiece, Pfizer's (PFE 0.28%) shares appear tentatively cheap. However, the pharmaceutical giant reached these levels because it has faced significant headwinds, resulting in a poor stock market performance over the past three years.Yet, what is the outlook for the struggling giant from here? Is Pfizer worth investing in at current levels? Slowly engineering a comebackPfizer's revenue and earnings have been inconsistent ove ...