Spoiler
During the GNR quest, I nearly crapped myself after that Super Mutant Behemoth came running over that pile of rubble at fast speeds.
The Centuars were really disturbing when I first encountered them. I was really wondering why it was called a Centuar. It definately doesn't look part horse.
The first time I saw a Deathclaw was west of that church to the west of Jury Street Metro. It was walking away, so I decided to follow after it with my Combat Shotgun out. After following it for a few seconds, it stopped walking. I knew before the encounter that they were dangerous. I went into V.A.T.S., and I shot it once or twice with the Combat Shotgun. It started coming after me, and then I walked backwards shooting at it. After a few shots I blew its head off, and I was lucky it didn't even hit me. My first encounter with a Yao Guai didn't go down nearly as well. I did what Three Dog told me not to do.