I've been running this in 5e and converting it on the fly. It's a great sandbox for both players and DM to get introduced not just to D&D, but to the whole idea of a "scenario" rather than a "story." There is no overarching plot to Keep on the Borderlands, just caves full of monsters and descriptions of how they relate to each other.
The reason I didn't give the module five stars is that the importance of not simply having all the monsters attack the first person to set foot in their lairs isn't really brought out. A novice DM may just run this as a slaughterhouse, which will make it a boring drudge right away. When running this module, it is essential to treat it as a living world and have the mosters behave in plausible, meaningful ways, rather than have them just sitting around, waiting to get into a fight.
[4 of 5 Stars!]