honestly, combat-wise, left 4 dead 1 and 2 both blow this game out of the water; hell even the original SOD does.
As you mentioned, in those games you have time to catch your breath and revive people before more Zs show up. and the Zs in the aforementioned games are less nauseating to fight, i know having been playing a little L4D2 lately.
in this game however; if you aren't careful, you're in for a one-way ticked to shits-ville with the amount, how many are bullet sponges, and the insta-killing assholes like the worms, and the one with the mouth that makes it look like a serious sam reject.
Edit:
forgot to mention, top off everything i spoke of with a crash, and having had enough, i deleted this turd of a game. try as i might to get some enjoyment out of this thing, i just gave up. unless someone can convince me otherwise, i'm done with dealing with this shitty game