The scotch doesn't seem to have impaired the script any, but it didn't exactly make it sparkle either. “The Blue Dahlia” isn't a bad example of the genre by any means, but it isn't a stellar example either. It's just a middle-of-the-road noir murder story about a guy who's accused of murdering his wife, but who actually didn't. The plot is as convoluted as you would expect from Raymond Chandler, but the ending doesn't quite make logical sense because Chandler sets you up to think that the murder was committed by the main character's shell-shocked best friend, but then he turns out to be innocent too.
The reason for this is that the Army didn't want to deal with the reality of damaged soldiers with PTSD coming home and committing crimes, so they asked for the script to be changed at the last minute. Chandler pulled it off, but the ending still feels a little bit arbitrary.