The biggest changes I'd say is there's a new class called the demon hunter, the ranking system has gotten a pretty decent revamp
https://cdn.gamer-network.net/2020/metabomb/newranked.jpg (Unsupported image host)
I know they made it more accessible for returning players by letting you have a free deck if you haven't played for a while but I don't actually know many details of it.
There's a new mode called battlegrounds that's very similar to auto chess/team fight tactics which I'm not a fan of but I know people are into that.
obviously there are the new expansions and the team behind the game are releasing nerfs/buffs more frequently now which is good when something overpowered is found.