I'm enjoying Tower Dungeon so far. The characters are not particularly complex, especially the protagonist. This doesn't seem to be Nihei's strong suite compared to world building. As I was formulating my response to this thread I came to the realization how similar the main protagonist and the overall story is to Knights of Sidonia. Both Tanikaze and Yuuva are outsiders that take on the call to action to fight some outside threat to their community and quickly become the person people depend on in their fight. One is basically Japanese Battlestar Galactica and the other is so far reminiscent of a Japanese Lord of the Rings, both literally involving necromancers coveting a jewel the protagonist is holding.
Unfortunately so far the characters seem pretty stiff and somewhat one-dimensional, much like the character is Knights of Sidonia. Though I feel like Tower Dungeon characters have slightly more personality. I do feel like Nihei was more interested in developing a fantasy world rather than coming up with complex character backstories, much like in Blame and Knights of Sidonia.
Despite the stiff characters, I am still interested in continuing to read the manga. His take on a fantasy word is still intriguing and I am invested in knowing what happens to the ragtag group of characters.