Edit: I forgot to mention that this is all from one of the copies of the gameplay vid on youtube.
- Marines as Jump troopers
- Landing dropships(?)
- NEW: Temporary/portable pylon
- Warping in units via Pyons
- NEW: Protoss self-warpers
- Siege tanks with less severe minimum range
- Different pattern of Nydus canal usage
- Green zerglings?
- More durable Zealots(?)
- NEW: Protoss mecha
- NEW: Protoss fighters
- NEW: Protoss beam corvettes
- NEW: Protoss Mothership
- NEW: Temporary super shield
- NEW: Protoss Black Hole Weapon
So it'd seem that slight elevation changes have become much less of an issue, at least once someone has upgraded sufficiently. Protoss air power has been altered considerably. They also seem to have gained at least one new unit which is roughly analogous to Terran Jump Troopers.
The temporary pylon ship would let you establish a well-defended Protoss base in a fraction of the time it would normally take, since you could queue up Pylons and other buildings simultaneously, as well as warp in units to defend the base.
According to some Youtube comments the Protoss mothership is overpowered, it seems roughly analogous to a Carrier, but is apparently also a spellcaster.
The Zerg Nydus canals are interesting - they looked scripted, but there were quite a few of them. Maybe just for dramatic effect, but it seems worth noting.
So I find it hard to believe that there's going to be no gameplay changes in Starcraft 2, given that the game isn't even to pre-alpha stage and the Protoss armada has already been redesigned.