A very powerful and gripping story, the flashback structure of the story is not revealed until the end, as it serves the cold, analytical way that the "hero" looks at his own life and his continuous string of failings, deceits and misdemeanors. His struggle is not so much with the drug but with his failed expectations in his own persona. Ray Milland's performance is astounding, and holds up totally realistic even 60 years later.
There is a lot of bitter humor in the picture which serves it very well and some great directorial ideas on how to convey ideas in simple pictures. My favorite was the little rings that shots of rye leave on the bar and how they multiply over time.
Definitively worth a re-watch and in-depth analysis.