If there is a problem with the Borderlands novels, it's that Claptrap isn't featured nearly enough. That, and they aren't really very interesting.
Borderlands is a video game series set on a planet called Pandora (not the one from Avatar). It's a hive of bandits and deadly creatures, irresponsible corporations and a bazillion different guns. The game is a straight forward shooter. You run around, shoot everything that moves, and collect whatever loot the guys you shoot drop. Is it violent? Ridiculously so. Is it for teens? Probably not, but that never stopped them from playing it. The games are firmly tongue-in-cheek and don't take themselves too seriously.
This is where the books (Borderlands: The Fallen and Borderlands: Unconquered) fall flat: they don't take the same tone as the games, even though the settings are the same and many of the familiar characters and creatures are featured. The novels simply aren't as... charming? Is that the right word here? As usual with video game books, the plot doesn't really matter. They exist to provide players with another opportunity to spend time in the gaming world that they love. This formula has mixed results: the Mass Effect novels got progressively better, the Elder Scrolls books were refreshing in that they weren't tied too tightly to the games, but the Assassin's Creed books were just awful.
Author John Shirley has previously adapted Bioshock, a game I didn't much like, but I loved the book.