Alex Delaney of Bon Appetit tells us that canned tomatoes aren't fully cooked or, specifically, they are cooked but not to the point we'd like them to be. When tomatoes are canned, they get soaked in hot tomato juice, sealed, and then heated to kill any potentially harmful organisms. Period. They are cooked enough to make them shelf-stable, not tasty. This explains why canned tomatoes taste somewhere between cooked and raw. You might have noticed that when you're making a tomato sauce for pasta - you can't just heat it up.
This method is a sure-fire way to add the pure flavor of tomatoes back.
Step 1: Separate the tomatoes from the juice.
Place a colander on top of a medium-sized bowl. Pour the can of whole peeled tomatoes into the colander so the liquid strains into the bowl below and the tomatoes are left in the colander. (Keep that liquid!)
Step 2: Cook the tomatoes.
Cook the tomatoes at the bottom of the saucepan or Dutch oven. The goal is to remove the water from the tomato solids and allow them to caramelize somewhat and concentrate their flavor. Less water and more caramelization means more sweetness, acidity and complexity.
Step 3: Add the liquid back in.
The tomato liquid will lose water content and concentrate over time as well.
By the way, I tried this method and it really does make a difference!