Since approximately the 1.7.9 version a big problem of gameplay appeared.
With the almost disappearance of the desert and above all jungle biome playing minecraft became hard and some interesting caracteritics (ocelot, jungle wood, temples...) of the jungle biome are lost. Playing pre release 1.8.2 in survival mode i traveled 5000 blocks in the same direction without meet one of this biome. So i create 20 new world without more result. That's all. I hope this problem to be resolve.