The game WILL be shipped complete. Co-Op won't be available day one, it is being planned for release after launch. That is why it won't be included, look at the promotional poster. GG is giving everyone free competitive multiplayer maps. You would think people would be grateful, seeing as how they are one of the very few studios to do so. $20 is a great deal for this kind of bundle, COD charges you $15 for a single map pack (boring recycled maps), whereas GG is giving 3 map packs, Ski...
Co-Op won't be available day one, which is why its not going to be included in the retail price. It will likely come out a month or two later. Also they are making all competitive multiplayer maps free for everyone, which is like a $40+ value right there. They said there will be tons of maps.