This DLC adds excellent levels and GLaDOS (and all the heckling that goes along with that)!
The combination of the Portal (game by Valve) graphics and GLaDOS voice/character into the Defense Grid world was excellent. While the DLC on the whole is really very good and recommended, the DLC needed some level-balancing...the very first level took me about 5 tries to find a path/solution that would even remotely work and, for me, was by far the toughest map of the entire DLC. A couple other maps in this DLC gave me challenges too, but that's part of the fun; only that first map, I thought was too tough, especially for a first map of a DLC.
This DLC is also unique in that it would come up with 'twists' during the level...it would remove a couple towers, or not allow you to build a certain type of tower, or only allow you to place command towers while it placed all other turrets, etc. This DLC made for unique set of challenges and a lot of fun.
Despite the 8 maps, however, this is a short DLC taking only roughly 2.5hrs to complete the campaign and that's including my struggling on 2 of the levels.
Not quite as good as the Resurgence DLC set (my favorite), but certainly a very nice DLC indeed. 8.5 out of 10