I'll be honest, I actually haven't seen any gameplay of this after that disaster of a reveal trailer, and my god, a side-by-side comparison really does go to show just how much more impressive of a game L4D is by comparison. It's the little things, like the way zombies charge at you, to their dynamic death animations, to the facial expressions of the survivors, to Source Engine props scattered around the environment that make L4D feel more "real" despite being a much older title.
Also "no modding support" is code for "we want to sell skins and DLC, just like with Evolve."