You can also play as NOD, simply take control of their main building, it will give you a feel for it if nothing else.
And don't discredit the hulking Avatar walker, you can use it to "eat" any other unit and gain that units abilities in addition to its main beam cannon.
EA is saving the Scrin for the game, you can find nothing on them anywhere at this point but a few teasers.
However, the game was made to not be a teching war. C&C 3 is set up to be over in less than 15 minutes of play. Which is kind of refreshing in a lot of ways if you want to just play a quick one, you can do so, without having to set aside a whole hour. And if you want to tech and have a long battle, that ability is there as well.
I prefer the 1 superweapon and long time limit. It basically ends the game now, as it would in real life. So, unlike in generals where you could have one out in 3 minutes and a full base defense, and nuke someone 5 times and still not kill them.....it doesn't work that way anymore. I loved generals though.. one of the few I suppose.
FWIW