Corrupter - New Unit
- An air-to-air combat unit.
- Rather than destroying it's opponents, it infests them an turns them into a stationary turret-like unit/building, making them fight their own allies.

Infester - New Unit
- As a battle support unit, does not have any attacks.
- Can move while burrowed.
- Can cast Dark Swarm: Seems to be the same.
- Can cast Disease: Creates and aura that damages the unit.
- Can cast Infestation: Can infest any building and create infested marines from them. The marines are slow, but fires similar to regular marines.

Roach - New Unit
- Ground unit that can regenerate HP at an incredibly fast rate.
- Requires powerful and concentrated fire to destroy.
- Has 90HP.

Overseer - New Evolutionary Unit
- Evolves from: Overlord
- Larger vision range than the Overlord, can detect invisible/burrowed units.

Overlord - Upgraded
- Can no longer detect invisible/burrowed units.
- New ability: Can neutralize resources or neutral posts.
- Can create small creeps.

Baneling - New Evolutionary Unit
- Evolves from: Zerglings
- Explodes on contact with enemy units or buildings

Swarm Guradian - New Evolutionary Unit
- Evolves from: Mutalisk
- Has an even longer range, and powerful against ground units.
- Can create broodlings that attack for a period of time.

Nydus Worm - New Unit
- Unit version of the Nydus Canal.
- Can create canals anywhere on the map.

Queen - Upgraded
- Created directly from the Hatchery
- Can only have 1 Queen at a time.
- Has many powerful abilities that are good for zerg and directs the defensive line.
- Can expand creeps or act as a defensive structure.
- [Ability] Deep Tunnel: Can move to any hatchery on the map.
- Can evolve and learn more abilities.

Ultralisk - Upgraded
- Can now burrow.
- Can now attack multiple units.

Old Units - Same
- Zergling
- Hydralisk
- Lurker
- Mutalisk

Where did you get all these details? Its not listed in the feature section of Starcraft2 website.