It is a Training area and a single Mission; I've finished it just now.
As you know, with only a single analog stick they had to 'adjust' how the camera works just like how Peace Walker had to adjust for aiming. The triggers rotate the camera left and right, and Triangle and X move the camera up and down. It seems awkward at first, but you don't really have to pan the camera up and down enough for it to be any issue. All the real "basics" are the same; CP points, base capturing, AP, command/action mode functions, potentials, etc. Here's an idea of the big changes I've seen (remember though, we only have one mission and a training pen to work with):
Weapons feel a fair bit more accurate now. In VC it felt like you really had to invest into R&D just to get a good ballpark accuracy at anything that might be considered mid-range. The analog stick feels like it's too sensitive, but the D Pad is very precise for aligning up your headshots after finding your target (the triggers still work to switch targets in action mode). So not a huge indication necessarily, but pulling off headshots and getting mid-range kills with tanks/lancers overall felt a lot easier.
No game over if the Protagonist dies. That could possibly change in the main game to the classic style, however.
Reinforcements are instant. This is a pretty big bonus, but they are also instant for the enemy as well; so combat might be a bit more intense now.
In the demo mission, the map can actually consist of multiple separate areas; capturing the base camp in the demo Map 1 also captures a Base Camp in demo Map 2. You can then send units to Standby (Retreat) and move them over to the second map; and likewise you may have a separate unit cap for each map section in a total combat map.
No Freesia, I will miss her.
I really don't like the protagonist.
I haven't seen anything of the new R&D, potentials, etc. and there's also supposed to be something akin to Social Links from the Persona series (or at least, that's what the intro cinematic leads me to believe) as the game runs on a calendar system. Overall I'm actually rather pleased; I'm actually only about ~25 hours into the first VC and there's quite a few things in this PSP version that I wish would have been in the PS3 version.