Warhammer 40k Soulstorm is the best real-time strategy(RTS) game that I have played. Period. Then we can go to Rise Of Nations Remastered HD Edition and sequel Rise Of Legends, Command and Conquer Generals with Zero Hour Expansion, Command And Conquer Red Alert 2 with Yuri's Revenge Expansion, Supreme Commander 2 With Infinite War Addon, Age Of Mythology Remastered HD Edition. Not to mention the excellent Conquest Frontier Wars a space strategy game which is very easy to learn and enjoy. Also I forgot to mention Warzone 2100 which is free to download from http://wz2100.net. This excellent game has such a diversity of units that you'll be playing it for a long time.... Other free to download strategy game are Megaglest: https://megaglest.org/download and 0 A.D. from http://play0ad.com/download/.
Other worthy entries include Warcraft 3 with Frozen Throne Expansion, Command And Conquer 3 And Expansion, Command And Conquer Red Alert 3 and Standalone Expansion, Anno 2070, Empire Earth 2 Gold Edition and Dark Reign. You should be having all the above games on your PC or have them on DVD's/CD's.
Now, lets go on to the Grey Goo review. It is a real-time strategy game featuring a meager 3 factions: Human, Beta and Go each with their unique tech tree. Graphics are OK and not mind-blowing.You will definitely need a good graphics card and a processor to boot. I suggest core i7 with and 2Gb HD card preferably Geforce or AMD quad core with 2GB Radeon HD crossfire enabled(CPU to GPU). Do not mix an intel CPU with an AMD Radeon Graphics card. A Radeon Graphics Card works best with AMD processor. Core GPU speed should be 1ghz, your physical RAM should be at least 4gb, you should be having a 160/320/500/1tb HDD with at least 50Gb free to play this game.
Units do not level-up as in Command And Conquer Generals which is a shame. The most horrible part of the game is the build part. It is very tedious. you have a limited number of slots, so you have to build structures called "Hubs" either small, medium or large which pave way to making more units up the tech tree. You also have upgrades as well such as the ability of aircraft to auto repair at the hangar.
There is a skirmish mode which you can play if you have finished with the main campaign. The skirmish mode seems to be borrowed from Warhammer 40K. Now in skirmish, the AI seems to bombard you with an army of like units which it has amassed. This problem is not limited to Grey Goo but to a vast majority of RTS games. This is very annoying to a seasoned RTS player. To make an RTS game enjoyable, there should be an option to limit the unit cap so that players who like to play with a few units, can set the cap to maybe 20 or 30 units. A diverse number of attacking units is good for A.I strategy also as in Command And Conquer Generals Zero Hour, the A.I. Generals "talk" to you during the battle in series of taunts, as you either do well against them or they make a successful attack.
In any RTS game, more focus should be on skirmish mode and focusing on people who like casual and enjoyable gameplay. Also there should be an A.I. that adapts to you style of play, attacks when you attack it, warns you when it is mounting an attack at you, challenges you to bring out your units for a duel and re-spawns after you completely destroy its base for infinite gameplay. Also there should be a whole variety of sub-quests or stuff to do within a skirmish game like destroy a particular raiders camp, rescue stranded units, collect some resources, assassinate a target etc., etc.
I hope some programmer reads this and make a game that really enjoyable and worth playing. This guy should look into the above games and infuse elements from all of the above into a great RTS game. He should utilize a game engine that can work on even low end PC's. Take a look at Warzone 2100 the game rocks even on low spec machines.
For me, Grey Goo is not worth it. I played the campaign and skirmish for a half hour or so, found nothing to draw me into the game and so I just uninstalled it from my machine and I don't think this game will make it to my collection.