Serving temperature makes a HUGE difference in the taste of a wine- in my opinion, it's actually one of the biggest factors in your perception of flavor. A cooler wine is less expressive; the flavors (as well as the perception of alcohol) can be muted, and tannins will feel tighter and more astringent on your tongue.
Wine's flavors come from aroma compounds —stereoisomers as scientists call them— that are released during fermentation. So, when you smell wine, the alcohol volatilizes (evaporates into the air) and carries these lighter-than-air aroma compounds into your nose.