Do Druids have other burst options? No.
FoN should be 4 mana for 2 3/3 treents. Same damage on it's own (comparable to fireball and other options), but weaker with the combo (12). Savage Roar is excellent the way it is, it fits a perfect niche, like power overwhelming or unleash the hounds. Plus this opens up the double roar combo without any modifiers, which, for 3 cards and 10 mana, is perfectly balanced for the 18 damage it would do.
I definitely agree, facing a druid means keeping their board clear for fear of that swing turn where you die. I really don't think should be nerfed. It's an epic card that's ok on its own. , however, is a basic card and I could see it being tweaked to be less powerful much like they did with . It's funny because they nerfed because of the sudden flood of damage out of nowhere. Yet, they introduced the same thing with , although that's much less reliable. Personally I don't think it needs to be nerfed, and that's coming from someone who never runs druid (I'm simply missing too many cards, including FoN). However this season (rank 3) and last (legendary), playing an overload shaman, druid's my worst matchup.
The combo is fine, however Hearthstone is going to suffer going forward due to having no way to interact on your opponent's turn to break up these types of crucial combos.
The Druid combo is fine because it's the only finisher he has. However Savage Roar can be a little strong but not as OP as a Mysterious Challenger. Force of Nature + Savage Roar combo is usually used when you want to finish your opponent, BUT if you use Mysterious Challenger anytime you already won the game doesn't mean you had 5 health and your enemy 20. Blizzard should stop focusing on older cards when their new cards aren't even balanced.