Ok, after a great deal of soul-searching and experimentation, I've concluded that I really like the overall Classic D&D moreso than AD&D (heresy, I know) and the d20 D&Ds. Further, I do believe that I prefer what I've seen of BECMI to what I've experienced with just B/X (nothing against B/X). I think I'll pick up some of the books when I get my next allowance*.
Next question: How hard are these to reference in actual play? I have read that there are some major differences (though only about 5%) between BECMI and RC. I have a PDF of RC, but it's pretty much just a reference book.
*After paying bills, giving my wife what she wants for her next sewing video, paying my daughters their allowance, and so forth, I get a hundred a month to blow on myself. Being the dad and sole income earner means that I put them and their needs and wishes ahead of my own. My wife and I argue about it sometimes because I will refuse it if we have something unexpected come up, which she doesn't think is fair. So, it's not really an allowance.
The Mentzer Basic Player Book has several pages in the middle that have just about all the info that a player needs.
The DM will have to make his own charts, though. Not a big problem, really, since Basic only goes to level 3.
The Castle Mistamere adventure is pretty good; amusingly weird and potentially frustrating. “Bill the Fighter decided to take a nap on the bed in this room, and now we can’t wake him! Hmmm…maybe if we carry him to this other bed in this other room, he will wake up. Hey! It worked!” Who would think like that? Also, the talking box. If I were playing, I would probably waste everyone’s time trying every thing I could think of to get the box to talk again, or to get it open. But, nope. The box asks two questions, then is silent forever after.
The second level dungeon is laid out, but the DM populates it with monsters and treasure, with a few pieces of advice how to do so.
The third level, Bargle’s hideout/cave, is for the DM to design completely.
Changing subjects, It wasn’t until a much later edition that they included a DM screen. It’s called the “Combat Shield and Mini-adventure”, and the pdf is $2 at Dmsguild/drivethrurpg. The info on the screen for PCs only goes up to level 14 (xp, spell progression, etc.), except for the thief skills chart, which goes up to level 25.
Necrotic Gnome has referee screen inserts available is pdf on drivethrurpg for $6, or $12 if you want the physical cards. Since OSE is a B/X clone, the info will only cover up to level 14 for PCs.
I made my own DM screen: