Other YMMV tropes applying to the series in general:
Adorkable: Claptrap. Even for a robot he's endearingly dorky.
Complete Monster: In the novel Unconquered, by John Shirley, Dr. Vialle is a Mad Scientist allied with General Goddess Gynella in her plan to subjugate Pandora. Using his SusDrug, Vialle drives entire villages and camps into lustful frenzies, making the males slaves to Gynella while the females are handed off to be raped by her armies. Vialle also performs horrifying experiments on countless people to test his new inventions, resulting in one subject tearing himself apart, and Vialle plans to ultimately betray Gynella herself for his own power.
Goddamn Bats: Rakks, similar to their spiritual predecessors the cliff racers, have an annoying tendency to attack then fly away to the point it is hard to hit their narrow, fast moving bodies.
Scrappy Mechanic: Arbitrary Maximum Range is in full effect and is particularly aggravating with sniper rifles, as the bullet just magically disappears after traveling a certain distance, meaning you'll always fail to hit a target more than a certain distance away even if they are holding still and right in your crosshairs.
Ugly Cute: Skags, when domesticated, still look like hideous lizard monsters but act like cute dogs.
What Do You Mean, It's Not for Kids?: The games are beautifully cel-animated, which may fool some parents. However, on top of the gory, bloody explosions, you have characters like a thirteen-year old girl who witnesses her parent's brutal murder and wants revenge, a monster who just wants to be accepted and loved by society, an assassin, and a prolonged scene of assisted euthanasia (in which after the father in question hypocritically guilt trip you by calling you a child killer). The game also deals with fairly complex themes like the dark side of capitalism, greed, drug abuse, corporate exploitation of the environment, and grief. The humor is also pretty off-color (though profanity is fairly infrequent). Oh, and there are lots of guns. 87 Bazillion, to be exact.
Woolseyism: In the French translation of the series, a literal translation of "Catch-A-Ride" (an automated service providing vehicle rentals) wouldn't sound very good, so the translators changed it into "Auto-loc", which includes a double-meaning where both possible meanings are as meaningful as the original. "Loc" is a shortened form of "location" ("rental"), while "auto" is both the shortened form of "automatique" ("automatic") and "automobile" ("car").