Aging Beer?

I recently opened a NOV 09 bottle of Founders Breakfast Stout. At a year old, I was hoping to see improvement. Truth be told, it was "bland" compared to the fresh Breakfast Stout. The flavors were mild, and the body was much lighter. Honestly, it just seemed like the beer went down hill. I stored the beer upright in my closet and it was not exposed to any extreme temp or humidity. Founders Breakfast Stout is a pretty big beer at 8% abv, so I thought it would have aged well. So here is my question... What beers/type of beer actually ages and becomes better beer?