I just tried the demo for Homeworld 2 and I was quite impressed.
Everyone that have played Homeworld before know how great that game was and the sequiel seems even better. I played the Tutorial and the two single player mission and here's some thoughts:
First of all HW 2 looks and works similar to the original, the controls are more or less identical and graphic, although better, is recogniceable. What have been changed graphic-wise is the level of detail; the ships are much more detailed and the now have additions like grappling arms on some vessels. You even play with an identical Mothership like that one in the original HW.
One change that you will notice early though the construction of modules. To build, for example, Interceptors you first have to build a Fighter Facility sub-system which will be added to you mothership as some kind of 'add-on'. It seems that these add-ons can be destroyed thus preventing you or your enemies to build a specific type of ships. Carriers also carry some of these add-ons. Research facilities are also add-ons and not free standing stations like in the original. Finally, you now have the ability to create squadrons of ships that will launch simultaneously and not one and one. If you build, for example, Interceptors you will build five instead of one but on other vessel types this might be lower.
For fans of the Homeworld series and everybody else here's a link to download the demo (141 MB):
http://www.sierra.com/downloadfile.do?mediaid=8216