I'm a die-hard fan of the gin & tonic (going so far as to insist, editorially, on ampersand usage instead of the written conjunction when writing the drink's name), and I know exactly how I like it: one part gin, one part tonic, juicy lime wedge squeezed and dropped in. But in certain contexts — and with certain gins — I've found that pushing the drink's flavor components to extremes can result in a drink that's entirely different in character, and often just as good.
That's the case in this Cucumber Gin Cooler, which takes the standard three elements of the G & T (gin, tonic, and lime), and boosts the citrus to a dominant role. Instead of the scant half teaspoon of juice you'll get from a lime garnish, each serving of this drink is made with the juice of an entire lime, which dulls some of the gin's alcoholic tang while still allowing its herbal notes to shine through. Shaking the juice and gin with slices of cucumber further enhances the fundamental flavors in the spirit: many gins have inherent notes of cucumber (some, like Hendrick's, are actually infused with it); the vegetable's summery flavor makes this drink a splash of sunshine on even the rainiest days. (Persian or Kirby cucumbers work best: they're firm-fleshed and strong flavored, standing up well to both the bruising they take while being shaken, and the long soak in the drink.)
A note on the cucumber slices: it may be tempting to nibble them out of your drink right away, but try to resist the urge. After several minutes' contact with the lime juice, gin, and sweet tonic water (about as long as it takes to finish the drink) they pickle ever so slightly, taking on a lovely crisp-sweet flavor. It may be unladylike to fish the slices out of the ice-filled glass using my fingers, but I've never been able to resist.