Jade druid has been around for a while now, and proven to be a very competitive deck.
With the recent nerf to quest rogue slower decks are becoming more prominent in the current meta and this is where Jade Druid is very strong.
Overall the deck's great strength lies in having an inevitability (an army of big boys) combined with flexible cards like Earthen Scales that can be used early to make favourable trades and maintain board, or later to gain massive amounts of armour.
Please note that Hungry Crab and Gluttonous Ooze are tech choices and can be replaced with whatever you feel is strong versus what you are currently facing. For example Yogg can be a great fun card and late game win in matchups where you fell too far behind, whereas Doomsayer has the potential to change a favourable matchup vs aggro into an absolute stomp.