Not sure "best ever," but new race, new faction ability (and a very cool one to boot), and lots of new ship parts make this a very solid value. I'd still but a couple of the LH DLCs above it, but very solid. Oh, and I know you said as for as sandbox goes, but the campaign map is pretty darn fun as well.

sorry androshalforc, the Snathi have always been squirrels. They were cuter in GCII, but still undoubtedly squirrels.

Yes, the best DLC so far in GalCiv3.  The Snathi are a blast to play as.  I imagine they'd be fun to compete with.  You just have to get into the evil squeeky voice mood before you load them up. 

I've recovered several tiny pirate ships and scrapped them for a few BCs each.  When I'm strong enough, I'll see about getting some of the larger AI ships too.  They seem to start with minimal hitpoints left, so you don't want to go to battle right away.

They're very much hated by everyone.  I see nothing but angry AIs out there, using much more energy in their distaste for me than called for.

It's refreshing.