Great, unique game; bad value.
Darwinia is an amazing RTS game that is unlike any other. The most noticeably unique thing about it is the obviously portrayed 3-D graphics that give you the feeling you're in some virtual 3-D world. The shading and lighting effects bring out the fact that the graphic engine is actually quite well done and that the squarish land appears that way for the reason of setting an atmosphere of the game.
The gameplay is also unique and very fun. Although the amount of things you can actually do is rather limited, it's still quite immersive and doesn't leave you bored. You can command your little programs to destroy the viruses and free the Darwinians. Sounds kind of corny but it is really quite fun.
The only problem that I had with this game was how short it was. I only found out after I bought it, that it was only a single player game. So I found myself having completed the entire game under 10 hours of playing, so that pretty much sums up the entire time I ever played it because really once you've beaten the game it's quite useless. There is no replay value at all unless you're a very patient person who can somehow manage to enjoy beating the simple levels again.
Twenty dollars isn't so bad I guess but I was really quite disappointed. If you have 20 dollars, and you don't mind spending it for about 10 hours of fun then definitely get this game because it's definitely very fun and unlike any other game you've played, but if you could spend your money on a game that you could play more, you should probably go for that.