It's actually supposed to be 3% on _all_ crits, and will be fixed to doing that again when 2.3 hits (i.e. a week). It's a 3% increase to total crit damage too, not crit damage bonus, which means it's a 6% increase before counting things like Impale.
Thundering Skyfire is okay but not great - the PPM is too low, and unless they've changed it recently it has a rather nasty internal cooldown and a relatively short buff duration.