This DLC requires me to undergo a bit of a mental adjustment. I'd gotten used to seeing Claptrap as Claptrap, an annoying little robot who tagged along on my adventures and somehow got the idea that we were friends. I'd forgotten that Claptrap was actually a claptrap, part of an entire line of annoying robots of unspecified function (the claptraps I'd helped in the main appear to be able to dance, open doors, and upgrade my storage capacity, so your guess is as good as mine).
According to the story Marcus tells when you first arrive at Tartarus Station (to a perceptive and critical kid who I think would be funny to meet in a future installment of the game), the Hyperion Corporation comes to see the vault hunters as a drain on the economy, so they reprogram a claptrap unit to become Interplanetary Ninja Assassin Claptrap and dispatch the characters in various subtle ways (such as spreading catty rumors). But then the INAC gains self-awareness and turns on its masters, so I'm called in to clean up the mess (the fact that I was originally marked for death by these people never comes up).
Mostly it's a fun excuse to kill claptraps, but it makes me wonder - where was the Claptrap during all this? He wasn't killed, but was that because he simply didn't get in my way? Was he actually the Interplanetary Ninja Assassin, who, in the end, was reprogrammed rather than killed? There was no hint of that in Borderlands 2, but it would be weird not to see at least some mention of it in the Pre-sequel (or maybe it wouldn't because it's a four year old optional add on to a game that has since had a sequel and four additional add-ons).
Whoever he turns out to be, the villainous claptrap is probably the best part of the DLC. He has the same mixture of juvenile humor and unmerited confidence that make's BL2's Claptrap such a hoot, and his popping in to comment on you deeds is always fun.
The worst part of the DLC has got to be the bosses. All of the enemies (after a brief opening mission) are mind controlled by INAC's technology (indicated by them sporting a weird dome on their heads and having their names changed so as to end in "-trap" e.g. "skagg-trap"), and as you proceed through the game, you will encounter -trapped versions of certain bosses - General Knoxx, Dr Ned, and Commandant Steele (who is really just a reskinned Atlas assassin). It's a little annoying having to replay all these fights, but what elevates this to a true complaint is the fact that, before you can get to INAC himself, you have to do a boss rush where you face them all again.
Recycling boss characters for the DLC is a little lazy. Doing it twice is just unforgivable padding.
It's not that big a deal, though, because, other than that, the story is pretty fun. You see Tannis again (though she's played more like a generic mad scientist than is entirely merited by her backstory as an insane archeologist), and Marcus is there (meaning you see him, in person, at New Haven, T-bone Junction, and Tartarus station, as well as driving the bus at the beginning of the game - does the dude ever sleep?), plus the new character, Mr Blake, is somewhat amusing. He's a bit drier than most of the post-DLC Borderlands characters, but he gets some good lines (like when INAC takes over a factory to build an army of claptraps and he complains about "the clear violation of Hyperion's patents and copyrights.").
Overall, I'm glad I played this DLC (though I had to fudge a bit and start it up on playthrough 2, because the recommended level on PT1 was only 37, luckily you can travel to the DLC areas right from the start of the game), and I feel well prepared to start playing the Pre-sequel tomorrow. I don't think I'll bother with the Island of Dr Ned or the Underdome, because I think I can probably go at least 18 hours without playing a video game.