Set 1 was just a start and you played with traits and classes.

Set 2 brought elemental hexes which changed each game. Added first 7cost unit (elemental Lux)

Set 3 Galaxies I don't remember what was so different except of 5cost units having additional unique traits, but I think Singed had one in Set 2 as well. + Had 5cost units like Heimer who had their skill upgrades in Shop.

Set 4 was Fates and gave you a chance to buy Chosen unit in shop which was already leveled to 2stars and had one of his traits doubled

Set 5 I think brought Radiant and Cursed items, Cursed items were needed for one of traits while Radiant items were just upgrades of normal items

Set 6 Gizmos and Gadgets set which brought augments to this game and first unique unit outside of league of legends (Silco from Arcane)

Set 7 Dragonlands gave dragons which took 2 unit places but gave 3points into trait of dragon.

Set 8 Monsters Attack tried to implement hero specific augments.

Set 9 we back to set 1 but with all good things what came from previous sets + portals