They tried something new and it kinda fell flat.
First of all, the story is bad. HS is a silly game but there is a limit to how silly you can be until i lose interest. Lets be real, who actually cared about Rafaam and his band of discount villains? It kinda butchers the WoW lore this game was once based upon.
The decks and OP hero powers they give you in normal mode were a bad idea. You just breeze through all the content in 5 min with no effort. Might as well give me the cards for free. I understand why they did it, to allow everyone to get the cards, but this kinda made me lose interest fast in the bosses. They weren't memorable.
And the cards themselves...ugh. They could have made a mini expansion that had the same theme as the year, but no, we got rejects from previous expansion that don't really fit at all with what the meta situation is. Winged Guardian made embiggen good, but besides that most new cards fell flat.