All the aged Imperial Russian Stout I have tried have been superb, perhaps you haven't kept them very well. Unfortunately the same can not be said for Thomas Hardy's Ale which has ranged from reasonable to Bovril. The finest aged beer I have is a larg-ish collection of Thomas Sykes Old Ale in various guises, from the old Heritage brewery. These have been consistently superb, and I only wish I'd bought a few dozen more when they were brewing.
Mark