The general outline of the changes:
Basic infantry has become more abundant and has a better damage to cost ratio then before, its vulnerability to attacks mostly didnt change though, with the exception of heavy infantry.
Vehicles and especially stationary defenses benefit from extended weapon range, stationary defense perfomance and armor overall increased making it more viable against the early rush tactics.
Tier 2 and tier 3 technology is more difficult to access and much more expensive to construct, however its perfomance is great making those units candidates for good micromanagement and making them an important tool against turtling players, some of them have also got additional special powers.
Some common sense changes: armor differentiation for armored (and unarmored) vehicles is made more significant. That means that tanks and apcs-buggies-mutated cockroaches are better armored in the front than from the sides and rear, bikes are especially vulnerable from the sides, vehicles with glass cockpits in the front are more vulnerable in the front (harvesters, pitbull), avatars are better protected from the sides, etc. For some units (like stormrider) the weapon has been modified.
Differentiation between tier 1 and 3 units is much higher than it was in the original game.
New units Include: GDI Lightninghawk and Light Orca, NOD Loyalist squad and Reconnaisance bike, you will also find new interesting special powers, like aerial missile strike for Stealth Tank.
some pics would be nice, that way we know what to expect.