How is that different? Here are three things, pick one of the three things to modify your deck and prepare you for a random set of possible foes (random bosses instead of random classes played by humans)
It's about as different as when a new set releases, we're now offered Knights of the Frozen Throne specific cards in arena now. If you want me to count Dungeon Run as a new expansion, sure, it's that. But it's not sealed or something.
I don't know how I'm supposed to be extra excited about the cards that cost 0 mana and start in your hand. Nonccg RPG elements in the ccg game, sure.
I'll play this, though. It's a new expansion. It's just one I have to play against AI which is likely to be less fun. I expect I'll get less out of it than Halloween.