I had the same problem with this book as I had with the one before, it is underdeveloped. There's a lot here that's interesting, the comedic moments made me laugh and the action was engaging, but without that development, nothing hit as hard as it should have.
The other issue I have is that the protagonist is woefully underpowered for what he's facing, and also is constantly depowered by the plot. While series like the Dresden Files have made their name by sending their protagonists into situations that are out of their weight class, I find those books only work because it feels like the protagonist is just out of their league, and usually because they underestimate themselves. In these last two books, there is no question, Strong is seriously out of his league. There's not a small gap he needs to leap to go toe to toe with his enemies, it is an enormous chasm.
To make matters worse, the author is constantly depowering him. Like the main character, I too have a strong interest in Wolverine's (from the X-MEN) powerset. This is because the idea of an immortal character is fascinating and exploring that concept is why I pick up books about that character. It is also why I'm interested in this series. Unfortunately, the author here has the same problem as many authors who handle the Wolverine character, they don't think you can create tension without the danger of death. That is a mistake.
Tension is created through conflict. The most obvious form of conflict is violence, and this is where this myth has come from. If someone can never be hurt, how can any violent conflict have consequences? However, that is not the only form of conflict. You can get conflict from something as simple as working against a deadline, or from facing an impossible choice, or from fearing for other people, or from any of a near-infinite number of story elements. By developing your characters and story further, you can easily write a story about an immortal man where you don't take away the one thing that makes him truly interesting, his immortality.
The problem with this author not doing that is that in every situation the protagonist might as well be a normal person because a loophole in his immortality is always exploited. This instantly loses my attention as a reader because I came to read a story about Superman, but instead, I got a story about
Super
man, and that's not nearly so interesting.
Overall these last two books haven't hit the mark for me. There's potential here but not enough to make me want to read more.