Project Legion really is a unique book. Jeremy Robinson has established that his works are a multiverse and brings them all together in this last, epic adventure. Personally, I have not read any of his non-Nemesis books but I did not feel lost. It seemed like I would have gotten a lot more out of the characters from his other books if I had, but it was not completely necessary to do so. While Project Legion feels complete in and of itself, readers will walk away wanting to know more about those characters. These are supposed to be the greatest heroes in all the multiverse and they pull off incredible feats. It would be like watching Avengers but having only seen the first Captain America film beforehand.
Because of the “Robinverse”, some things in Project Legion do not 100% make sense. Some of the other heroes that pop up are just kind of there to help fight. You do not really need to know too much about them. Others are as key to the plot as the Nemesis characters have been since Project Nemesis. Not just characters either; concepts from the other books (presumably better fleshed out in those other works) are also crucial. Robinson has said that Project Legion was meant to more or less wrap up his currently works as a whole so that he can start fresh on new series, so for folks who have read his other books finishing up those plots was probably pretty satisfying. If anything, Project Legion makes readers want to go back and look up Robinson’s older works.
For the characters from the Nemesis Saga, Project Legion is very satisfying. Without real spoilers, it does end how you would expect. Good triumphs over evil and the characters finally get the peace they have fought for. The narrative throughout is similar to the other books, humorously told by Jon Hudson. There are still plenty of pop culture references throughout, both directly and indirectly, but that was toned down a bit. By far, the Nemesis Saga is the best kaiju series for your bookshelf. While some parts of the series have been weaker than others, overall it is very solid. Any fan of fantastical sci-fi and giant monsters will love this series. Here is to hoping that Robinson’s next kaiju book, Unity, can live up to Nemesis, the Queen of the Monsters.