Let's compare it to Duress, which is going away from Standard soon (not that I care much about Standard play...).
Duress has 1cc, allowing it to played on the first swamp land-drop. A good first-turn Duress can often stop a valuable player strategy for at least a few turns. At the very least, those Parallax Waves and Tangle Wires won't be hitting the table for some time.
Addle is delayed a turn with its 2cc. Like Duress, it can't target lands (they're colorless), and unlike Duress, it can't target artifacts either (they're similarly colorless). So, those Tsabo's Webs and Tangle Wires are safe. However, it does have the ability to force the discard of creatures, an ability which Duress does not have. That means Blastoderm, Lin Sivvi and Thrashing Wumpus are all heading to the graveyard.
I believe that Addle's ability to take out creatures is what puts it into an entirely different class from Duress. Duress was the combo/game-breaker smasher. Addle is the setup-breaker, removing key creatures as well as annoying spells and enchantments. So it can't target artifacts. Other than that, imagine it as a combinatiion Duress and Ostracize (an ignored card because of the power of it's better cousin Duress).
I for one believe it is a much better card than Specter's Wail. So, you have to choose a color. In the early going (which is when this card's effect is important), you'll ge your colors right at least 75% of the time due to the number of gold card going around. And that's if your opponent is playing multi. With mono, you can't go wrong at all.
While I still think that the best first turn effect is an Unmask or Coercion, Addle would be for me an excellent follow-up.
