A new trend in Champagne is "Brut Zero," where no dosage is added to the finished product. Dosage is the sugar solution that is usually added to Champagne just before the final corkage. While it can be used to add body and complexity, it's also used to mask grapes that didn't ripen enough (a huge problem in the cold, rainy Champagne region), or to counter too much acidity.
However, some Champagne makers are skipping this final step, making a bottle of bubbly that tastes purer, with more mineral components than crisp fruitiness. It can be an aquired taste, but it's definitely worth a try if you are a Champagne lover.
If you want to try this style of Champagne, look for "Non-Dosed" on the label. Piper Heidsieck, among other prestigious producers, are now making this style.
These non-dosed style would pair really well with shellfish, including oysters.