Brought tower defense game to whole next level, spent hundreds of hours on it with friends or solo (this game more fun co-op), now on Steam sale for 75% off for 2 days. Get the Complete Pack for USD$6.24 (normally $25) or 2x Complete Pack for USD$9.99 ($40) or Complete Franchise Pack (OMD1 is better for solo) for USD$8.74 ($35).
No matter which pack you choose, if you like tower defense game, you'll love this!
ninja edit: price/USD
Honestly, considering how often this goes on sale and how many times it's been bundled, this is a fairly mediocre deal. That's not to say the game isn't good. This is a fantastic cooperative focused game that's great to play with a friend. It's possible to do everything solo but the game is a lot harder that way.