Having played TA and Sup Com, I had been very excited about Sup Com 2. However after playing the demo, they have changed everything that made the other games great.
First things first, they have ruined the way the economy worked. Now replacing building lots of energy and mass production you will just build a bunch of stupid research facilities to increase the speed in which you can "tech". Also changing that you have to have resources before building further makes the game just like any other crappy RTS out there.
Units: Now there are less than 15 units (air, land, and navl) combined to choose from, outside of experimental, once again this has destroyed what made the previous games great with diversity of units. Not too mention the fact that there is no mention of end game artillery or nukes. Removing both of those again destroys the franchise.
Graphics: They look terrible, the maps are clunky at best. The best analogy for water was that it looks like a bunch of units skating around on ice. Everything looked cartoony if I wanted that I would play starcraft.
Gameplay: Eng not being able to help build, takes for ever to make units, and only have 3 air units to choose from just sucks. As far as the storyline goes, I could care less cause I only use it to learn the game initially, because I would rather play online.
I'm totally disapointed. At this point I'm hoping that they will patch or have an expansion that will do what TA:CC did for TA. The only other hope is that the demo is just lacking the end game units I'm looking for.
One last thought from reading these posts, basically if you like Supreme Commander 1 you were capable of micromanaging the resources and techs and you wont like Sup Comm 2. On the contrary if sup com 1 was too "complicated" for you, then you will probably like Sup Comm 2's dumbed down economy, units, and overall gameplay.