Best part about this game, they got Frank Klepacki doing the music. Really makes a worlds difference.
I've mostly been just goofing off in skirmish mode against AI (my computer atm is a piece of shit, I'll be upgrading it over the summer). Its honestly a breath of a fresh air, its a Command and Conquer style RTS through and through, but I really like what they did with the UI, all tech upgrades, unit production and building production are automatically tied to QWERTY so you can instantly start rebuilding your army even while across the map.
Its a much slower paced RTS than say Starcraft 2, you don't need to macro OR micro that much to be successfull (just enough micro to avoid your troops getting eaten by goos). However, due the different unit types (arty, aircraft that work like C&C aircraft, etc. etc.) you can't just blob up your army into a deathstar and attack move to victory. There barely any skills for units either, almost all of the tech upgrades are passive.
To some this might be a downside if you're looking for a much more competitive RTS, but if you enjoy more strategy than APM benis comparisons you'll enjoy Grey Goo. Its nothing groundbreaking, but its a fun RTS something which RTS fans haven't had in years.
The biggest downside though is its $50 at the moment, theres some bugs in the game especially in matchmaking, and its not very well optimized, at least for me.