OSE is recreating B/X so that has lower HD than AD&D and later editions. I started with B/X and I am a fan.
Here are my issues with it though:
Thief skills are designed to fail until high levels, leaving thieves as MU's with no spells but leather armor and backstab. I'd prefer something like Necrotic Gnome's
B/X Rogue as a variant to replace them.
1st level magic users have one spell. No casters have cantrips. Useful at will cantrips are great.
Healing is rare, clerics do not even get a spell slot until second level. I would want an unconscious condition at 0 HP and some healing mechanism like 5e HD or 3e reserve points.
Low level hp, being at risk of being one shotted or overwhelmed quickly in combat for more levels. I would want a boost to hp like +5 to everybody to start.
Save or die. The B/X rule book sample description of an adventure had a 2nd level thief Black Dougal check a chest for traps, finding none he opened it and found out he missed his find traps check. He got hit with a poisoned needle and missed his saving throw so instantly dead. He did everything right and died from a single missed save. Even though the save gets better with levels poison is a save or die single roll threat at every level. I'd prefer save or unconscious or save and something else.
Energy drain. Blech.
I remember a lot of whiffing at low levels. PC attacks are not that accurate.
It is a good rule set that is quick and will not require a ton of character sheet referencing.