Moldvay describes halflings as “small, good-natured demi-humans averaging only 3 feet in height” who are “outgoing but not unusually brave, seeking treasure as a way of gaining the comforts of home which they so dearly love.” (B10) Halfings roll 1d6 for hit points, and get to use any weapon or armour small enough for their frame. More importantly, they get good saves (reflecting uncanny luck?), +1 to hit with any missile weapon, -2 AC bonus vs. creatures larger than man-sized, +1 to initiative, and the ability to hide (90% effective outdoors and 2-in-6 in the dungeon).
The force of Tolkien is strong in this one. If, for example, you wanted to run a Bilbo in B/X, the halfling class (as presented) makes more sense than a thief—not only because Bilbo wasn’t a proper burglar, but because Bilbo isn’t a professional at all—he’s a homemaker. Nevertheless, he acts fast in a tight spot, avoids attacks from big foes, and hides well. These aren't things he trained to do. Rather, he naturally possesses all the defensive tools needed to go into the wild, grab some loot, and come back to home and hearth relatively unscathed.
Put another way, given the halflings’ love for creature comforts, those few who actually do go on adventures manifest exactly what Moldvay describes, but little more. Halfings aren’t interested in being the strongest fighter or the most powerful wizard. Instead, they want to get enough gold to apportion their little hobbit holes in costly array, while avoiding direct confrontation as much as possible. That they’re limited to 8th-level supports this—they’ll adventure just enough to retire in comfort, but the whole build-a-strong-hold-and-carve-out-a-dominion drive really isn’t a priority. 
I think this is a bit staid for a PC. I suppose it does a good job of depicting the aberrant behaviour of a few individuals in a race of what largely seem to be gentleman farmers. But the same might be said of non-adventurers of any species. So I like to up the stakes a bit and push halflings out of the Tolkien mode.
A race of diminutive men, halflings are cosmopolitan traders, explorers, merchants, and adventurers. Generally amicable, usually jovial, and always cunning, halflings appreciate the finer things in life and work hard to avoid hard work. The "tall-folk" (i.e., any non-halfling) tend to judge halflings by their size, which is fine by most halflings, who rely on the fact that they're frequently underestimated.
Advancement Cost 
Move Rate: 8”±1d4
Wound Limit: 1d6
Abilities: Diplomacy, Mettle, Observe, Sneak
Perks: Lucky, Marksman, Nimble, Quick Draw
Flaws: Restricted Weapons (small only)
Special Perks (Sperks)
Comfort Food: Meals prepared by halflings reduce a wound's severity by 1
Creature Comforts: Halflings always pack a bit more into their kit; gear packs of any sort have 8-16 (1d8+8) uses
Disarming: Underestimated as a threat; foes target the halfling only if the halfling attacks (or is seen to attack) first
Fleet: Improve Parry vs. larger foes by level (melee only)
Indiscernible: Sneak rolls made with 2d20; take best result
Good Man in a Storm
Not so much an Ability, but a way of life reflected by Diplomacy, Mettle, and Observe. Despite my desire to move away from the Tolkien stereotype, these are Bilbo-inspired, and I think they work as talents any race of diminutive physical stature might logically develop. Bilbo was all about diplomacy, with Thorin, Gollum, Bard, even Smaug. Mettle is almost a requirement for anyone who fights giant spiders when they’re rather have a quiet fire, a pipe, a pocket handkerchief, and cakes. Finally, there’s not much that gets past Bilbo—remember the secret door on Thorin’s map, secreting the Arkenstone, or following the Wood Elves’ routine to help the dwarfs escape.
I consider this a mix of Tolkien and Moldvay, with just a dash of my own to make halflings “fit” into an adventuring context. A lot of settings have tried to breathe new life into halflings, so this is by no means re-inventing the wheel, but I do think it helps explain the halfling as an adventurer as presented in B/X. So, Bilbo anyone?
Cook’s Expert rules note that halfings can build a stronghold whenever they have sufficient coin, and that such establishments may attract a community of halflings, but my sense is that this is just to keep in line with the high-level options of other classes.
My target AdCost is 8 (2,000 XP / 250 = 8).
Moldvay, Tom, ed. Dungeons & Dragons Basic Rulebook. Lake Geneva: TSR Hobbies, Inc. 1981.
Smale, Erin. Chimera Basic. Atlantic Highlands: The Welsh Piper. 2011.