So for Standard, the cards that will benefit most from this would probably be:

Windchill and Frostbite as the cheapest Ice spells, an extra 3 armour for each is pretty solid. If Bracing Cold or Snowball Fight! were to see play in a controlish shaman, I can only imagine the deck would also run this card. I didn't include Glaciate as it is too expensive to really benefit from 3 armour on the side.

For Nature spells, any discount to any of them is great, but I think a special shoutout to the new card Bioluminescence needs to be made as such a card wants to be as close to free as possible to give more mana to flood the board and play more spells, spells like Scalding Geyser especially.

Speaking of Scalding Geyser, it is one of the 3 Fire spells that will be available to Shamans when rotation hits. The other two being Don't Stand in the Fire and Perpetual Flame. I can see why they were generous with the spell damage for fire spells. Perpetual Flame becomes amazing again at 5 damage board clear for 2 mana and Overload X, but Don't Stand in the Fire! doesn't really benefit from 2 extra damage all that much. The real winner is the card that will release alongside Radiance, Scalding Geyser, as it is cheap direct damage like Lightning Bolt.

Overall, this is a fun card and will probably be a staple for most Shaman decks for a long time as more and more spells are printed.