Dark Dungeons is the Retro-Clone version of BECMI rules as Labyrinth Lord is the Retro-Clone of the B/X rules. Some of the example characters and the name itself is a riff on the old Jack Chick tract attacking D&D.
I never bought the Rules Cyclopedia or the BECMI rule sets, so I don't know how closely the two mimic each other, but I happen to like it for its Skysail approach to Spelljammer.
I'm using my cell phone to post this, but I'll add the link in a few hours when I get home. I was just starting this tread to generate some opinions. Like it? Hate it? Would you use it in addition to LL/AEC?