For me it was the hype of Claire and Chris in a jet at the end of Code Veronica vowing to finish off Umbrella that had got me hyped for RE4. I have been an RE fan from day 1. I remember all the hype and early RE4 demos, the one with the hook guy. Even then it looked awesome. I bought a Gamecube primarily for the RE series.
RE4 at the time just got everything right. The weapons, the shooting, the inventory system, the graphics, and the enemies were all above what I was expecting. And man was this game long. TLOU and Uncharted 2 are the only games in recent years that have such excellent pace much like RE4.
Also I think RE4 was the first of its kind in the 3rd person genre. The way bullets reacted to enemies, was phenomenal. The Mine Dart was the coolest weapon ever. Exploration and level of detail were never seen at that time. I never got to try the HD version. Maybe I should. I cannot wait to dive back in to the REmake HD version when it comes out.
I hope Capcom can go back and realize what made this series so awesome becuse RE5 andRE6 were nothing like the other games for me. Too much shooting and explosions going on. The story is now all over the place and I just don't care about the characters. I know they were trying to capture the western audience but they already had me. I don't know why they strayed so much from a proven formula in RE1-4