Guys!! It is simple! When I started vaping approximately 6 months ago, I vaped store bought flavors, and had the same issue. I slowly began starting to make my own liquids. I will never look back. Its cheaper, funn-er, and you can make the flavors to your taste.
What is causing the lack of flavor? It can be two things; One, the flavors you are buying have low %'s in the mix, causing that blandish flavor. A lot of e-cigarette stores in my town water down their flavors with water, or use less flavor concentrates to make more money. Or two, they simply haven't sat long enough for the flavor to marinade and bring out it's true potential.
I started blending my own liquid about 2 or 3 months ago, and have never been happier. The trick is to make your liquid blend, then add some flavor until it tastes like it needs a liiiittle bit more flavor. Once you reach that point of where your flavors are a little less sweet/flavorful than you want, you let them sit in a dark cool area (such as a cabinet in the garage or a closet) for at least 2 weeks. The longer they sit, the better they get. It's in a way like a steak! Once it's marinaded longer, the final product will be that for satisfying. Gove it a try!