There may have been something wrong with your can, but I definitely remember the first time I tried san marzanos because of a similar feeling. There is something about their flavor that does seem metallic when compared to the typical california tomatoes that we have all grown up eating. Over time the flavor grew on me, and now I like it very much, especially once cooked. You might want to try another brand of SM before you give up on this type of tomato all together, but the "less sweet" SM flavor might just not be for you. Also realize that not many people are willing to pay $5 for a can of tomatoes when there are plenty of choices at their supermarket for $1. Because of this it is very easy to buy a can of SM that have been sitting on the shelves for 3 years. Avoid any dusty looking cans, or any stores that don't seem to do a lot of business.