The bright, shiny, red, smooth, uniform-looking tomatoes that show up in grocery stores have been hybridized to enhance production and durability at the expense of flavor. There isn't anything wrong with eating grocery store tomatoes in terms of health, but once you taste the sweet, brilliant complexity of an heirloom tomato, you understand right away how different and special they are.
If you can't or don't wish to grow heirloom tomatoes yourself, and if you don't have green-thumbed and generous family or friends willing to invite you over for grilled bruschetta this summer (oh, the tragedy!), you can usually find a whole rainbow of heirloom tomato selections at your local farmer's market.
Here in Michigan, the first heirloom tomatoes are just beginning to ripen, and tomato harvests will extend into the fall. Happy tomato tasting!