If you own Defense Grid on Steam but haven't purchased the 4 Resurgence Map packs, here's your chance to get them for free:http://store.steampo...mmersale/prizebooth/
You just need 3 tickets to redeem for the Resurgence Map packs. And you can get them easily by doing any 3 the following:
1. Join the official Summer Camp Steam Group: http://steamcommunit...com/games/summercamp
2. Link your Steam profile to your Facebook account. (from your profile page)
3. Make a comment on the profile of somebody on your friends list.
4. Write a review of a game (such as Defense Grid!)
5. Post a screenshot of a game.
6. Play a free game demo.
Those are probably the easiest way to get 3 tickets, but there are more ways than that and more to redeem the tickets for than the Defense Grid map packs.
And if you don't want to bother with the tickets then you can buy all 4 map packs for about $2 since they're on sale.