Labyrinth Lord is hands-down the best classic B/X retro-clone/simulacrum system available; the only way to get a closer experience to the original Moldvay/Cook is to buy the original Basic and Expert books!
When you add in the material from the Advanced Edition Companion, the overall game plays more like the "Best of the LBBs" than Advanced D&D, which I feel is a definite feature, not a bug. The two volumes together have everything one needs to play for decades of campaigning.
Even with all the improvements in the new, 5th Edition of D&D, Labyrinth Lord is the best way to introduce young players to fantasy role-playing. As with the original, the system is clean, simple, and easy to understand, yet leaves wide vistas open for the imagination, on the part of the player as well as the Labyrinth Lord.