Untimately: Plate armor, dwarf saves, fighter attacks, +1 initiative, +1 missile attacks, plus a convenient hiding ability, with no XP penalty; the only downside is d6 hit dice instead of d8, but that’s only 1 hit point less on average (and you still die in a single hit at first level). Not being able to use long swords is a long-term disadvantage, but they have high survivability for a low level character.
Huh, interesting. Something to think about, as I have based a human ranger-type scout class on the halfling (pretty much just reskinned removing the size related qualities and adding a tracking ability).
Presumably it would also be harder to find halfling-sized equipment. The lower hit die is a pretty big disadvantage though.
Untimately: What’s the difference between your human ranger and the explorer? The explorer is pretty closely modeled on the b/x halfling.
Oh, nothing really. It’s an idea I’ve been kicking around from before I knew about ACKS, but the association seems obvious to me given the halfling’s wilderness abilities so I am not surprised that more than one party has come to the same conclusion independently. My version is more vanilla B/X because I’m still not sold on skill systems.
But yeah, pretty much the same thing.
Actually, my first take was to replace the halfling with a monk:
http://untimately.blogspot.com/2011/09/halflings-monks.html
I finally decided that the ranger was a better fit, though I am still quite fond of the dodge-as-save mechanic for the monk.
Given the links in that post, it’s likely I got the idea from here:
http://bxblackrazor.blogspot.com/2009/08/how-bilbo-baggins-ruined-everything.html?showComment=1249625561492#c554994535242188190
If one insists on letting demi-humans advance beyond their level limits, he could rule that they get -50% of XP.
Rather than a level cap, maybe an XP cap (like 1,000,000 for example) could have been used, then each class would have a different level limit, and each member of the party would cap out at the same time, rather than some party members capping out long before others.
Given the links in that post, it’s likely I got the idea from here:
http://bxblackrazor.blogspot.com/2009/08/how-bilbo-baggins-ruined-everything.html?showComment=1249625561492#c554994535242188190
APM: If you read that thread, I’m the “Alexander” who posted on Aug 10, 2009. 
Personally I think the key is to give humans something shiny. In my campaign they get an extra proficiency and slight advantage on attribute rolling (3d6 drop lowest then add 6 for two attributes of choice…demihumans only get it one attribute and it’s racially coded). So far I have 3 to 2 humans vs non.
Alex: it’s a small world, especially in the OSR.
Charlatan: Since I was thinking about it again after this post, I did write up a draft from my notes if you are curious:
http://untimately.blogspot.com/2012/03/scout-draft.html
Sorry to clutter up the thread with my house rules. Feel free to delete if you feel it is off topic. I would PM it to you but this forum doesn’t seem to have such a function.