I will make a review of the Genshiken unvierse soon for my page, but basically it's like this:

Genshiken:
The dynamics inside the inner universe of the otaku world and it's clash with the external world.

Genshiken 2:
The dynamics and changes of the personal universe of each otaku regarding the changes in the dynamics of his niche community triggered by adaptation to society standards.

Genshiken Niidaime:
A faggot joins a group of fujoshis and now wants to fuck a past member of the group.