Sins is the first rts game I have every played...
I started with turn-based stragegy games (alpha centauri, civ 3) and then at some point started with the total war games (shogun: total war)...over time I moved to more recent turn based (civ 4, galciv II) and total war games (rome and medieval II)...
Like you, I was very hesitant to buy sins...
But I did...
And I am damn glad I did too...
Coming from turn-based games, sins at first was very different and I had to change how I play...RTS games are about time-management and intuition while TBS games are more about deep-thinking...nevertheless I adapted and Sins is my favorite game...
If you happen to know someone that own sins, try and play their game...of course, if you do find out you like it, please buy the game, don't just use their impulse account...
I turned 6 of my friends onto sins by letting them play my game...all 6 of them fell in love with it and purchased it on their own (another reason why DRM doesn't help make more money)...if you can actually sit down and play it (even if its just the demo), I have a strong feeling you will like it...
I'd say that liking the space genre is more important than liking RTS...I came from GalCiv II as well, and I very much like both even though they are very different...