I'm sure Doom's gunplay is just fine, but all combat in the demo was so room-based (and I've heard it's similar in the full game) that unfortunately it's not nearly enough to carry the game. It's kind of funny, because that's very deep in the game's core gameplay - more or less exactly what's being praised here. I don't necessarily need anything fancy extra to the gameplay but constricting combat to small arenas (with lockdowns) is simply not that fun to me.
To each their own though, I suppose. Like I said: gunplay seemed fine, and it seems that definitely not everyone minds the rooms.