Minecraft 1.5.2 Version -

Implementation of "social" zombies that could summon reinforcements when attacked.

—the first truly clean, white building block—which launched a thousand "modern house" builds on YouTube. Minecraft Wiki Final Legacy Minecraft 1.5.2 Version

For the first time, automated item transport and sorting became native features rather than modded dreams. The Redstone Comparator: Minecraft 1.5.2 Version

You still used a Fortune III pickaxe on diamond ore, but now you could build a Beacon (introduced in 1.4). With hoppers, you could automate gold farms (zombie pigmen) to fuel your beacon, something that required manual grinding previously. Minecraft 1.5.2 Version

While 1.5.2 was technically a bug-fix update, it served as the stable bedrock for the massive "Redstone Update"

Fixed incorrect level calculation when renaming items on an anvil using non-English languages.