Firstly, i just wanted to say, im so glad i was able to play the original RE4 before the remake was announced. Heck, i still remember it being a MERE RUMOUR.

This entry in the RE franchise was the first to have the over the shoulder view and include more action-packed gameplay. IMO, this game felt like a bridge between the old and the new RE, as prior to RE4, it was more on puzzle solving and really trying to survive. Then after the success of RE4 it led to it being implemented into future games.
This new gameplay made the overall RE4 experience fun, as with the new camera angle, it almost feels like you are accompanying Leon on his mission or even feel like the player IS Leon. The addition of a shop via the merchant was a nice addition as the merchant felt like a person existing in the story (whilst still not disturbing the plot) rather than it simply the player buying, selling and upgrading equipment from nowhere. Although action packed, it still has that "scary" element to it that RE is known for.
The only thing i didn't like about the gameplay is that the controls (moving camera angles up, down, left, right) felt "restrictive". Though i can understand it is an old game.
This game has some funny moments and sometimes questionable moments, a product of its time. But that's what made the game memorable, especially Leon being a complete dork.

Plot wise, it is a new story addition to the Raccoon City incident. I could say this could be a standalone game.

Overall, RE4 is a fun game!