Anyone download Dungeon Defenders. I've been couch co-op with my wife for the last two weeks and it's uprisingly addictive. It reminds me of the early EA Lord of the Rings games where you had levels where you had to fight back hoards of enemies while maintaining your defences. Even on the lower difficulties it's easy to get the adrenaline pumping when the hoards start marching. Check it out.
As for not taking advantage of this promotion.
Even if you arnt into a particular game it would still be wise to download all of them. By doing this, they will be recorded to your download history as a purchase and you will essentially be able to re-download it any time you want to play it or just try it. For example, in the rare chance something happens to your on-disc copy of AC2, you will "always" have a means to play it this way. Same goes if you have no intrest in tower defense, RPG games.
Better to download it for free, delete it off the HDD, and always have it available to you than not download it and have to pay to have it made available to you if you ever have the notion in the future.