I've heard from many faithful coffee drinkers that flavored coffees are just terrible. Not because the taste is terrible, but because the whole concept of adding flavors to coffee is disrespectful to the coffee. Coffee has such a wonderful flavor on its own, why mess with it?
How do they get the flavors into the beans, you ask? The process usually involves treating the freshly roasted beans with chemical flavorings (sometimes natural, and sometimes not). The fact that the coffee is processed with chemicals is a point against them. Since they are going to be treated anyway, quite often the beans are not of the highest quality and the roasting is haphazard. In other words, it may be a delicious drink, but it's still poor coffee.
The aromatic nature of the flavors tends to give the coffee a very strong smell, but the flavors don't always translate well into your cup. This is another place where quality comes in. A poor quality flavored coffee may smell great, but it won't have much taste. If you enjoy flavored coffee, at least get some that has been made from well-roasted, quality beans.
Many folks choose flavored coffee (compare prices) because it's too time-consuming to actually create a drink with a host of ingredients when you're in a rush. But a shot of syrup can quickly and easily add a new taste to your coffee. Or add some spices to your ground coffee beforehand. A bit of cinnamon, cloves, vanilla, or other powdered spice can be added to your ground coffee. Just brew as usual.