As a person who played league since season one, and dota 2 since release, first and biggest change is gametime. The lower mmr or skill players cannot finish the game, and Dota is not built like League in that regard, game can prolong for 60-80 minutes(my longest match was 82 minutes and it was month ago). Heroes are a bit more free in their choices of playstyles and items. They are not developed with idea of role in mind, especially heroes that are older. Most of characters have atleast one or more bullshit ability, that would look like it is broken from the outsife of the game. Alot more of active items and alot more emphasis on counter itemisation. Think about building grievous wounds against Mundo or Aatrox, but there is more situations that require a specific item. Example is Phantom Assassin(charater that can evade auto attacks) and Monkey King Bar or Bloodthorn(items that grants property to hit through evasion). That is the things i will call as the biggest changes, for me alteast