The Good: Brilliant dialog and characters, brand new weapons, environment, and enemies, level cap raised, interesting dungeons
The Bad: Initial dialog with doctors drags on forever, mostly consists of fetch quests, mainly for energy weapon specialists, usual engine bugs
New Vegas has been struggling in having solid DLC that stands up to the Fallout 3 releases. Old World Blues is the best of the three so far even for just the excellent dialog, great characters, and huge new world. Old World Blues has you going to a drive-in that teleports you to Big MT. Once inside you meet some strange doctors who lobotomized you and you are on a quest to stop the evil Dr. Mobius and find your brain. Old World Blues takes a whole new approach to Fallout DLC by removing your spine and heart and giving you perks at the start. There are new weapons, enemies, and a whole new world to explore.
There are also a lot of great dungeons to explore such as the X facilities which have things such as new armor, testing facilities that run you through a series of courses, as well as other hidden items like new recipes. My favorite part of the whole DLC are the excellent new characters that are inside The Sink which is your little safe hub inside the dome. All the appliances have hilarious personalities such as the evil toaster, crazy miniature robot, the perverted fertilizer, and the seductive light switches. Sound strange? That's what makes this DLC brilliant. Even the doctors have great personalities and the whole story has some twists at the end so you really get a punchy fulfilling story and ending.
The new weapons are some of the best yet such as the K9000 Cyberdog gun which actually barks when you shoot it thanks to the dog brain attached. The Sonic Emitter pistol is probably the best thanks to the upgrades you can find for it to enhance the power. Unfortunately this DLC is really best for people who specialize in energy weapons and melee because guns are hard to come by. Old World Blues also raises the level cap so you will have a change to maybe dumps some XP into energy if you are weak in that area.
The new environments are great such as the canyons that have giant red crystals which is a huge change from the brown wasteland. The new enemies are challenging such as the robo-scorpions, lobotomites, and other weird creatures lurking around. I highly doubt you will be bored with this DLC due to so many things being different from the other ones. All I have to say is that the dialog and characters are probably better than the main game and are just top-notch.
There are a few problems such as the initial dialog with the doctors will take you a good hour to get through its entirety. While the characters are very interesting you'll start getting antsy to start exploring. Most of the quests are fetch quests and this really kept the score from getting a solid 9 because I wanted some pre-scripted stuff or just more unique quests. Most of the quests consist of getting technology for The Sink and Dr. Klein. This kind of gets old after a while, but the quests drag you through most of Big MT so it'll help you encourage exploration. The usual New Vegas glitches and bugs are still ever so present, but the dated Gamebryo engine can't really be saved at this point. Old World Blues is a must buy even if you skip the past two because the good 12-15 hour storyline is just brilliant.