I haven't played it yet, but I really enjoyed the original Doom, and I am encouraged by how much of the original design philosphy stayed intact in the new installment (medkits+glory kills encourage you to stay on the on the offensive and on the move, minimal hitscan weaponry and smart enemy design discourage just staying in cover, keys and secret powerups encourage exploration, and there's still Carmack's story mentality ("story in a game is like story in a porn movie - it's expected to be there, but it's not that important"))

OTOH, given that I already have the original doom, is the new one really worth it? I mean, it's good, but it's not exactly going to beat the original at it's own game...