Lots of things were different in the DnD Next playtest, with things like martials getting a variety of manoeuvres, to casting in armour still not being allowed as a holdout from earlier editions. However one of the biggest differences was the sorcerer, which was an entirely different class concept altogether.
We only saw the draconic sorcerer, and only up to level 5, but it has almost nothing in common with the final sorcerer which we got later on, appearing for only a single playtest packet and then vanishing again until the final release of 5e.
The class was an arcane half caster, with a d8 hit die, and proficiency in all weapons and armour. Rather than spell slots it used 'will points' similar to the variant rule in the DMG. What really set it apart was that it would gain the abilities of its subclass as it spent those will points, becoming more like its power source as the adventuring day progressed. So for draconic you would gain claws and scales after spending 3 and 10 willpower respectively, turning you more melee orientated over time.
Sadly we never got to see what the other subclasses would be, or what would happen past level 5. But I found the class concept fascinating, and not really alike to anything we have in game currently.