The plastic playset is still around, regardless of all the articulated, detailed toys that come out today. Check out http://www.playsetmagazine.com/ and http://www.playsetaddict.com/ and you will see this hobby is alive and well. Also check out http://www.barzso.com/, http://www.conteco.com/, and http://www.sdsoldiers.com/ for the newest playsets hitting the streets.
Anyway, a company called Treehouse released plastic aliens and Colonial Marines between 2003 and 2005. There was a playset, and Swarm Packs. The buyer didn't know what was in the swarm packs, but they included aliens, marines, eggs, and storage boxes. I bought a few dozen swarm packs, put in a McFarlane Alien Queen from AVP, and here is the battle! The queen is not in this photo. Also, the variant figure in these swarm pack was a white/translucent alien, displayed here in the top middle.