Its the movie that made fast zombies popular from that point on, and there was more than enough restraint when it came to how many zombies were on screen. All the C tier zombie movies in the past 15 years that have fast zombies, there will be dozens or a hundred zombies on screen. At that point there's no fear.
What the fuck can one or a few armed individuals do with a mob of fast zombies around them? There's no hope whatsoever, you're fucked from a million different angles. When main characters are able to escape that scenario, all drama and tension legitimacy is lost. I have genuinely thought "well, I'd accept death at that point" in the garbage, million zombies sprinting everywhere movies.
28 Days later has incredibly intense scenes where one or two zombies is fucking terrifying. There's hope, there's a chance of not getting fucked, but the room for failure combined with that glimmer of hope is what creates tension, fear.
While I think Dawn of the Dead is okay, World War Z is a dog turd garbage fire in comparison.