I think the new snapshot is great. It adds new mobs. One issue I found with it is that the Kelp acts as air. Any entity in it falls down to the base (including Squids). It also allows nighttime mobs to spawn. They will spawn underwater in kelp blocks.

HOW TO REPLICATE
Make a world with the seed 4451472365338212581
Tp to -170, 34, 209
There will be plenty of mobs in kelp.