For many years, Divine Spirit + Inner Fire combo has been a staple in many Priest decks, especially budget variants. Now, Blizzard offers us a legendary that just happens to cast Inner Fire on all minions. This is a really interesting design, and quite a powerful one.
Imagine you're playing all those cheap cards with lots of health and 1 or 2 points of attack, such as Silverback Patriarch, Mogu'shan Warden, Public Defender, etc. And suddenly, they all turn into these overpowered creatures that are really hard to remove. Not a bad move, Blizzard, not bad at all!