I'll push back on Keep on the Borderlands. B2 is just so very overrated. It's boring.
B1 is terribly underrated, and B3 (at least in the orange cover incarnation), B4, X1, and X2 all deserve every last lumen of their glowing reputations.
Jennell Jaquay's classics (like Dark Tower and Caverns of Thracia) are even better.
I have complicated feelings about B2.
I will start by saying that I do have incredibly fond feelings about it because of nostalgia. And I think that it does a good job of setting up the "canonical" idea behind a lot of OSR- the base, the wilderness, the "dungeon."
But there's two major problems with it.
A. From a structural perspective, the Caves of Chaos will be entirely dependent on the DM's choices. If the DM runs it as "every room is separate, and doesn't react to what happens next door, and things don't change over time," then it is just an example of the most rote and boring dungeon crawl.
On the other hand, if the DM runs it as a dynamic place, the low-level adventurers can easily and quickly be overwhelmed and killed.
B. From a modern perspective, there's ... well, there's an issue involving "women and children," if you know what I mean. It wasn't until I pulled it out to review and run for the aforementioned teen group that I noticed this ... and then I couldn't unsee it. I am not judging others, by the way, but I realized that there was no way I could run that adventure for that group without re-writing those parts, and I chose not to run it.