Big, colorful fruity drinks are easy to like, but they're also limited. As your palate becomes more sophisticated, you might find you take more pleasure in simple drinks that showcase, rather than hide, the flavor of the spirits. The ultimate expression of that urge are spirits ordered "neat," which means it comes directly from the bottle at room temperature with no ice, water or other mixers.
When and Why
Low-cost utility brands of liquor are seldom ordered that way, because their flavors aren't usually subtle or complex enough to stand up to scrutiny. Spirits ordered neat are usually mid-grade or better, such as single-malt whiskies and well-aged rums or brandies. Bars typically serve them in an old-fashioned glass, though at home a tulip-shaped glass helps concentrate the spirits' aromas for your enjoyment. Adding a few drops of water can enhance the flavor and aroma of good liquor without diluting it noticeably, but it's best to order your water on the side and add your own.
Neat vs. "Straight Up"
The terms "neat" and "straight up" are sometimes confused, though there are clear distinctions between them. "Neat" is only ever used for single, unadulterated spirits. "Straight up" can be used with plain spirits -- in which case, it means the same as "neat" -- or with mixed drinks. A mixed drink served straight up is prepared the usual way, then strained into the glass without ice and without garnishes. It's still a simplified beverage, but not as spartan as neat spirits.