I finally got of a bottle of green Chartreuse, so decided to do a side by side comparison to a couple of the substitions recommended on this sub. We tried them straight and in a shaken Last Word with equal parts green liqueur, maraschino liqueur, fresh lime, and Ford's gin.

The depth of character of Chartreuse was unparalleled, both by itself and in the cocktail. There is a woody tobacco/leather character that completely cuts through and makes a Last Word really stand out as something unique. Both Escorial and Dolin Genepy made adequate cocktails, but they were missing that central character. Escorial was sweeter than either and had solvent notes in the aroma that were distracting when sipping it straight. Those largely disappeared in the cocktail, so it still worked okay. Genepy had a better aroma, though there was a menthol character and a lingering artificial sweetener-like tang afterward. As substitions, they worked about equally well/poorly.

Anyway, right now I am thinking that there is no real substitute for green Chartreuse. Also, although I enjoyed a Last Word, after having Chartreuse straight I find it difficult to want to mix it with anything. I probably would use Genepy or Escorial for future incarnations of the Last Word.