I think counterspells are interactive in that both players act/react, but interactivity is NOT what most anti-blue players gripe about. What they really mean when they say "Counterspells are uninteractive" is "When my opponent plays counterspells, I don't feel like I'm even in the game." There are many games vs control that go like so:
Player A - plays land, mox, 1cmc spell
Player B - missteps
Player B - plays land, ponder
Player A - plays land, spell
Player B - FoWs
Player B - plays land, mox, ancestral self
Player A - plays land, plays bigger spell
Player B - mana drain
Player B - plays land, Jace TMS, brainstorms
Player A - plays land, casts spell (not a threat with Jace), resolves, casts real threat
Player B - Gush, FoW
Player B - mox, tinker for BSC, brainstorms with Jace, time walk.
In that game, Player A hangs around a few turns and there's plenty of interaction. In reality, Player B was solitairing and Player A was basically draw/land/pass for all intents and purposes. Player A may well have never sat down at the table and would have been as much "in the game."