Defense grid 2 is, as it stands a competent and quality tower defense game.The follow up to Defense Grid: The awakening takes the same formula and expands slightly upon it. Why mess with something that works?
The core game play consists of destroying waves of enemies that are trying to steal your power cores as they travel into the map and out of the map in a predictable fashion. This is achieved by placing any of several different towers in the way of the enemies, rerouting them around the map as you choose. Enemies often come from/to different entrances and exits. Killing waves of enemies awards you money to spend on new towers and upgrades to your current ones. This is very consistent with the original Defense Grid, and can be very satisfying. There often is a point of no return where you have upgraded your towers and the last several waves are trivial. The early few waves are usually the most important.
The largest difference in the game play is the addition of the Boost tower, which is a passive tower that can have a normal tower built on it. As a result you can augment the tower that sits atop it with skills like damage boost and the ability to view invisible enemies. There are also optional choices to change your orbital laser skill to allow other things like making extra money when used.
Graphically, it's a major upgrade form the original. Better animations, a cleaner experience, and sharper response. The audio is a lot of banter back and forth between the various AI buddies you have that chat with you during the alien waves. I usually turned the audio down and listened to podcasts as it's not very interesting to listen to.
In the end however, while Defense Grid 2 is a quality product, it failed to capture me the way the original did as it's ultimately just a retread of the original. And while the concept is strong, it's just did not capture me because it's not new to me anymore. At $24.99 on Steam, it's an OK buy if you haven't played either the original or Defense Grid 2, considering the original is inexpensive and still an entertaining buy at $9.99. If you are into this type of game and can grab it for a steal durring one of the Steam sales, that would be much more worth it.