The flashback of the Forerunners fighting the Flood has to be up there with the best of them though. Didact and his squad in Class 20 armor facing a team of Combat Forms in near-equivalent suits fighting a Bullet Time battle in the middle of a nuclear explosion.
This troper disagrees. The moment MC puts on Didact's Class 20 armor (OMGWTF?!) and begins to throw down against Demogorgon? Yeah. That.