Chapter 3-1 getting out of that one area on the boat where they trap you , hell that whole free roam area is fantastic.
Conveyor belt fight, YES. You are moving along a belt with freaking explosive canisters everywhere, majini throwing dynomite from above, shield guys coming from the front, awesome.
Spinning elevator fight, how awesome was this, a spinning platform and with loads of enemies you have to shoot at a distance. Lining up that shot in a sniper rifle while spinning is so rewarding.
Giant laser room in chapter 4-2, having to avoid a super death beam is always awesome. Makes it even better when you can take out the laser controllers, loved finding that out.
Great balls of fire, all of a sudden a room fills with huge rolling flaming balls, and you have to get around them to the door in a certain time, its so short but awesome.
Licker rooms, hell all of them. My favorite is the one where its two long hallways and you can walk past them as they crawl up the ceiling and stuff. Tense stuff, of course you can never really get passed them without alerting them. Licker temple entrance was awesome but a huge pain.
Pre final wesker battle against the two reaper and two chaingun guys. The first time I played it I actually killed the chaingun guys without ever going to the turret.
Execution ground, hey I am on a raft, I wonder if anything is going to... EAT ME AHHHH!
Chapter 2-3 AWESOME.
Puzzle room, very well done.
And of course the boss fights especially Wesker ones.