Very nice. Citrus, obviously, is the predominant flavor; however, this is not very sour. It is actually very balanced as is. Used Cointreau as my triple sec.
This is certainly citrus-y and slightly sharp, what with the equal proprtion of lemon juice. Based on an old 80s cocktail book recipe, I have also tried this with Curaçao - Giffard's is a lovely opaque orange colour, and find its more complex flavour goes very well with the vodka and lemon. To my taste, the De Kuyper Triple Sec version ideally needs a little sugar syrup.
Correction: the Giffard is an attractive transparent orange Curaçao (not opaque). Thanks for the notification - the newly rebalanced ingredients look to be a very enticing proposition!