My initial reaction was same as OP. I was looking forward to something a little more new and courageous with the gameplay...theyre playing it safe and sticking with the same basic formula. Fine.
i like the open world idea as a fun factor - but at what cost to the immersion and story. D1 was intense because it was you, alone (or 1 to 2 max) descending into hell. Hows the story line going to play with 100 heroes running around - will they ignore it or will the world set that context? The trailor gave me home for a good story again, I just hope the gameplay can hold up even tho its unoriginal.