My thoughts on the demo, for what it's worth:
First thing I noticed was the performance, what a difference from the original. I can run the game at max with AA and 1440x900 without dipping below 60 FPS with V-sync on, and on my measly setup that's quite an achievement on behalf of GPG.
The graphics style has become slightly more cartoony and colourful, and in my opinion looks better for it. Even a small skirmish with lighter units is an absolute joy to watch, especially knowing that each projectile and unit movement is being calculated in real time.
The new tech tree system is great, it means that early units can be just as useful in the end-game, especially with a few upgrades. A reduction in the number of different unit types isn't even noticable, especially with the knowledge that you'll be getting 27 different experimental units to mess with come next friday.
The only issue I have is with the resource system. Although it's great that you can't spend the mass/energy you don't have (less time worrying about eco), it also means that you can't queue up even a small handful of units without half of them being removed because of a lack of resources. The same applies with buildings, you can queue up a number of different structures but if you suddenly run out of resources everything you've spent ages queueing up disappears and you have to wait and start all over again. This defeats the purpose of reducing the need for micro-management, one of the core objectives of SupCom 2.
New maps are much more dynamic, the campaign seems more involved (but still just people talking in small boxes in the top corner, not exactly the wonderful storytelling which was promised by the arrival of Square Enix in the games production), and overall I can't wait til release day but there are a few issues which I'll have to either get used to or hope that they get streamlined slightly.