As a first-person shooter I don't think slow zombies, on their own, really work. They're not a threat unless you have extremely limited ammunition or are otherwise too occupied to mow them down. Fast zombies can be plenty unsettling, mainly dependent upon their surroundings to produce the appropriate effect. This is why L4D2's atmosphere is considerably less suspenseful than L4D's in many respects: the scenes tend to be better-lit (daylight vs. night) and...well, more comical in some respects. The carnival is the obvious example of that, of course.
The fear zombies inspire comes from the shock/horror of being undead and all that, yeah? But as gamers...we've seen worse. We're sorta used to that, I think. It'd take something more than just "But they're undead!" to produce the desired effect. Personally I find the idea of zombies that can actually chase me and, even worse, work in packs exponentially more disturbing than barely-animated corpses.
Oh, in reality even the slow-moving zombies would be terrifying, no doubt, but I'd be much too concerned by the sprinters rushing at me covered in blood to even notice their slow-moving friends shuffling up the driveway in the background.
Priorities.
All that said, he's got the right idea in referencing a "different kind of strategy." Like I said, the issue with slow zombies in the L4D context is they aren't a threat given your equipment and abilities in that game. If the issue of ammunition were made more important you'd have to be more frugal in your shot choices. This makes the vast numbers of the horde more of an issue given you don't really want to spend much time up close and personal with them if possible. You'd have to weaken melee weapons a bit as well, most likely, though I'm not sure how to do it best. Limiting the number of zombies you can kill in one swing to two or three, perhaps, instead of basically "everything directly in front of you?" You need to make them more durable to make up for their lack of speed.
Additionally they need to be more dangerous if they ever DO reach you. In L4D we're told the survivors are immune to infection; this immediately removes the usual "bite" attached to zombies. We're used to knowing that if a zombie gets its teeth in you, that's it, you're done, end of story. Maybe it'll take you a few minutes to a few hours to turn but it's a foregone conclusion: you are a zombie-in-waiting. The L4D games (I don't know Dead Rising, never played it) lack this sense of danger - the main threat is from the special infected against which you cannot defend yourself if caught instead. Perhaps if attacks by the infected lowered your resistance in addition to doing damage there'd be a more urgent need to find booster shots in addition to medkits and the like. It would only take one bite to start the countdown of infection, a countdown that drops faster the more hits you take and requires one of those shots to get boosted back up (or perhaps simply stopped at whatever value it reached while falling on the higher difficulty levels - no recovery, only a return to stalled infection state).
As for comedy...eh. I think the interplay between characters is all the comedy that's really needed to break up the dread now and then. Adding silly props and the like just seems like too much, but then I'm not much for slapstick in action games, I guess.
