KleenX MC PvP has changed completly since 1.8
In Beta, armor had really bad durability, even at diamond and it blocked a small percentage of damage.
In 1.0, armor gained much more durability and block damage percentage. This is also why warriors were nerfed hard but kept being OP in the start of DG. (Ex: Goon went from full iron + dia pants to 2 iron, 2 chain, 1 dia)
Potions (1.0) let fights last much longer and represent a major factor in MC and HC PvP (A fire resist. pot can make you near immune to pyros and reduce caster dmg a lot)
Enchantments is a decisive factor in MC PvP, the player with highest level sharpness sword wins. In HC enchantments are used for their knockback by casters, the fire by melee classes and looting by farmers.
For non-PvP changes:
The Redstone Update that simplified redstone by far.
Villages ans Villagere (TESTIFICATE!)
Nether Fortress, Nether Quarts, Blazes
The End, Enderdragon boss
Tons of new building blocks (Quartz, Smooth Sandstone types, Wood types, Stone Bricl types etc.)
Lots of stuff has happened since 1.8 Beta, but I can agree that 1.6 was dissappointing.