So for the past couple days I have been working on networking using the Lidgren library.
I was never a fan of Unity's networking so I decided to just work from the ground up on this. So far a person can download the server and start it, the game will register with the master server and players can query the master server for a list of games.
I don't believe players should be bound to dedicated servers provided by the developer. This eliminates LAN capabilities as well as custom servers the likes of which TF2 and CS:S have.
Eventually I do want to expand the game servers and client to be expandable with mods (such as new tower "builders" and new NPCs).
Currently I have it setup that players can only gain skill rating when they are connected to an official non-modded server.
Hopefully by the end of next week I will have it so players can join a game and play against each other.