It has been said before, but Sins feels cheap for featuring no campaign yet presenting the player with three different races and some backstory in the manual and introduction cinematic. Sure, it was done on a limited budget and I'm glad the money was spent on polishing the most fundamental aspects of the game, but aren't your pockets full now Ironclad ? 14th best-selling PC game of 2008 isn't that bad. 
Then, the voice-acting is so-so. "No ledge acquired" says the Advent UI voice. What ? Then, those extraterrestrial races should sound a bit more extraterrestrial. Adding some cheesy reverb isn't quite enough. Starcraft wasn't produced on the biggest budget ever AFAIK and its voice acting is a pure delight. So please get it right next time.
The music is quite good though. I'd like to know who did it. "Upbeat 2" is a really cool track, I was humming it all day long after one of my first games. So keep it up! But try to make more realistic use of vocals; when I play Advent at some point there are ridiculously high notes sung by those synth vocals and it just highlights their synthetic nature in a very cheesy way.
I've detailed my thoughts here already : http://www.neowin.net/forum/index.php?showtopic=737042
