Generally speaking, the higher the elevation the coffee is grown at, the more complex the coffee becomes.
Higher elevation coffees develop slower in cooler temperatures with larger climate swings resulting in a denser bean. This slower growth allows the bean to develop longer in the cherry resulting in a coffee that has more sucrose. (percieved sweetness). You get brighter acidity and notes such as florals and bright fruit.
Lower elevations coffees develop quicker and tend to be duller, with earthy tones. Because they are less dense, they don't tend to store as well and lose flavors quicker.