They have (of course) fixed a lot of bugs AND they have put a lot of new biomes!!
Including: Savanas,Stone beaches,Ice beaches,Ice spikes,Disco moutains.skyworld(note Notch said you have to have a beefy computer it's really laggy but still cool)and a lot more.
They also added new fish:clownfish,pufferfish,and salmon.
Snow biomes no longer have snow but instead extreme hills now have snow on them(they made elavation) MORE BELOW just look at this link it shows all the new features!! :D:D:D:D:D
Link: http://www.idigitaltimes.com/articles/19781/20130905/minecraft-1-7-update-snapshot-13w36a-introduces.htm