This series has become my favorite LitRPG. Carl and Doughnut are both awesome, and I love the relationship that is being built between them. Other characters are getting introduced now, but slow enough that I have time to learn to appreciate each one. The story is all about the 3rd floor, and that is different enough that it allowed for some big changes from the first book so it still feels new and fresh. There is just enough mix of politics in it that makes you remember there is an outside enemy that they are dealing with, and is used perfectly to set things up for future books. Honestly, this is just really good.
If you like LitRPG, you need to try this series.