Oh, it most certainly isn't bad when you can only counterspell once per encounter (or even twice per encounter with the paragon feat), it's when you can do it at-will with the epic feat that it starts becoming problematic. At best, you're making a solo with Spells spend its actions for nothing _and_ getting a free use of your at-will out of it.
Now, another thing I noticed is that you have the power noted as a Feature. As of Essentials, WotC themselves seem to be categorizing all powers as either an Attack or Utility (for example, the Mage cantrips), not sure if you want to follow their lead on that.
Too subtle. What exactly are you getting at here?(there's a hint in the name "Vancian Mage");