I’ve written two posts about my opinions on B/X D&D.
What I don’t like about B/X:
These are the main “dealbreaker” features of B/X that I don’t like. I also don’t like the “nickel and dime” approach to bonuses and penalties typical of B/X and other post-OD&D editions and clones: 1-2 on d6 for this, 1-3 for that, +1 to +4 on d20 for this other… I hate the idea of having to look up what to use for a specific situation, which is why I use a minimal number of mechanics and move away from bonuses and penalties in my own game materials.
I will add, though, that B/X might not be as bad as other games in this regard; I don’t have a B/X book, but if the B/X clone Labyrinth Lord is any indicator, almost all the rolls are 1-2 on 1d6 or 1d20 attack/save rolls, but there are a sprinkling of modifiers, plus the ability score bonuses that I’ve ranted against before. Still, it’s no AD&D or WotC D&D when it comes to a very rulebook-oriented, just-about-everything-has-exceptions approach.
So, do I hate B/X? Probably a little, but that shouldn’t matter to people who love it. Would I run B/X, or a B/X clone? Definitely not. Would I play it? If I didn’t have to learn any of the quirky rules, I wouldn’t mind it, I suppose. I’d be forced to pick something other than M-U as a class, though, because of the weird approach to spells.
But this leads into another comment. I embrace the principle “Players should never have to learn the rules. Most rules are for GMs, as an aid to creating and judging situations.” But judging by the way many people post on blogs or forums, there are a lot of people who think players should be rolling all the dice, should know what dice to roll when, should know what target numbers they are aiming for, and record these on their character sheets. So if I were asked to play in a B/X game, I would definitely need to ask some pointed questions to determine if this GM is one of those bad GMs who places the burden on players.