Gal Civ 2 is a turn-based strategy whereas Sins is a Real-Time.  Gal Civ 2 has waaaaay more depth than Sins.  I love Sins and Gal Civ 2, I think if you like one you will probably like the other too, even though they are quite different. 

In Gal Civ there are many more races than in Sins and you can also make your own race to play as (or against), you also get to make your own ships designing them completely from scratch, which is totally awesome and of course missing from Sins.  Games in Gal Civ can take a very long time to play (weeks or months) depending on what settings/map size/number of opponents etc you use.

ok, have to be honest, the very first impression was "eww, why do people talk so highly of this?"

It is VERY overwhelming if you just dive in and try to figure it out. However, after watching through the tutorials, and actually reading the manual a bit, and giving it a second chance, I can say this has potential for some awesomeness. Adjusting to the change of pace is a challenge though. Is there any way to speed things up, especially at the beginning? Or do I just need to focus on single tech trees and not try to get everything available?

Other winning strategies? Bah.. diplomacy is what you use while you are researching bigger guns

It took me a looong time to really wrap my head around this game.  Now it's my favorite.  Stick with it.  And read this: 

https://forums.galciv2.com/104908