So, we are touting GC2 as the tutorial for GC3. Interesting tactic.
I do agree, though. If you like GC1 and are interested in GC3, it is very probably worthwhile to get a copy of GC2. There is a lot of fun to be had there while waiting for the Alpha developers to tell us it is okay to think that GC3 is fun, too. (They are so strict!!)
Most of the people in the alpha are long-time fans of GC2, even GC1. Pointing the ones that are new to the series to GC2 helps everyone by giving us a common frame of reference when discussing new things, changed things, things that we think were better off *not* being changed, etc. There's a lot of reference to the Civ series and other strategy games, but GC2 is the closest analog to what GC3 will eventually be.