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It is my favorite Sorceress skill too and works extremely well with a controller setup. While I do wish it had more than one synergy, it does allow an easier choice to spec into Energy Shield for a more defensive hc build.
A nice skill, poorly implemented and basically very unsuitable for other abilities.
Too slow as a primary skill due to CD, and as a secondary skill, it lags behind other abilities, making it difficult to use effectively.
The only good thing is that you only need one synergy, as Frost Mastery is not absolutely necessary if you include other trees.
This allows you to create a hybrid of FO and Charged Bolt, for example. It’s not really that strong, but it plays quite smoothly.
Otherwise, FO is half-baked.
It still plays okay with Blizzard, at least you don’t need FCR here and, thanks to RW Doom, you can put only one point in Frost Mastery, thus maxing out the damage from the Frost tree through all synergies.
Otherwise, it still works reasonably well with Glacial Spike fully skilled, but it only serves as a side effect.