That was actuly good, but I see stuff missing.
1. If you want to make a zombie series, get zombie skins and put them on, it will improve a lot.
2. Ricky hears someone scream and comes 20 minutes later?
3. Camera shots - Dont get the same place with one shot, do it from multiple places for example : When Ricky gets in the bus, change the view so he will be walking inside the bus towereds the camera, when he is about to get out, put the camera behind him showing he is leaving the bus.
Take a few camera shots all around, not just from 1 point, it will make the video more intresting.
Except of those 3, your video was good.