I hadn't played in nearly three years until about a month ago. I had no clue about the new cards, combos, etc... I bought the welcome back pack because it was cheap and said fuck it lets go.
I am playing a very budget Demon Hunter deck - pretty much everything you get from the story to unlock it and crafted a couple of needed cards from the dust I had from old school legendaries.
Plat 5 feels good and while it can be frustrating, everything has an answer or you just got RNJesus'd the wrong way.
You could go play wild, arena, BG, Duels or just casual.
I think the game is fine and I have next to zero new cards.