If you could add anything...

[mopb3]

Mo' Creatures dolphins don't look absolutely terrible.

Are they controllable? That'd always be the hard part

 

[13scooter13]

it would be cool to have hostile and non hostile mobs for water. like sharks or something. maybe more animals that we could tame to have as pets. but without using a mod for all of this.

 

[Zor95]

I think...

I would like to have the biome code programmed into blocks rather than the area, except for deserts.

 

[Artagan]

Birds. More music. halfsteps of all materials. stairs of all materials. thirst meter along with hunger. Some sort of physical mail system instead of chat based. Emotes (waving, smiling, frowning, anger bubbles, etc etc). Automated builder villagers that build buildings for you when you give them a certain amount of materials and payment. Horses for fast land travel. Dolphins for fast underwater travel. Shields that can be held with swords. Different kinds of arrows (flame, ice, poison, slow). New biomes that reflect a more mystical nature (crystal forests, burning pits/volcanoes, giant mushrooms, trees grow in a more random fashion at certain sizes, etc etc etc). A trade system with a confirm button. Musical instruments. different color beds. dream sequences when you sleep. barbarian villagers that attack everything and anything. True alchemy, the melting down and mixture of many different metals and alloys.

I could go on for hours. haha

A lot of this, plus dragons and flying machines like hot air balloons.

EDIT: and the Aether.

 

[JocelynReed]

Obby movable by pistons