You say every RE fan should play it, I say every gamer should play it.
The premise I thought was pretty funny. Save the president's daughter. Nice. Don't worry though, the plot gets much thicker than that and although it doesn't have huge twists, it's still way better than what games usually offer.
The level design is fantastic. Both modern and ancient settings are provided. The enemies are interesting and generally not too repetitive as they change appearance while becoming harder. The weapons are nice and varied, with many upgrades available. The puzzles are definitely too easy for anyone with experience.
The game's main strength lie withing its innovative gameplay. Shoot enemies from a cable car, escape a tsunami on a jet ski or drop giants in lava. There are tons of new, fun, ways to deal with enemies in this game that go well beyond the shooting routine.
I have very few things to say against the game but one of them is pretty important, which is why it doesn't get a 9.5. I found the shooting controls to be pretty horrible. For one, you can't move and shoot at the same time which becomes a bother in areas where you want to "push through". Aiming speed is a bit slow but this is balanced by the fact that enemies aren't exactly comets. Even so, enemies in close range can be hard to deal with a handgun which is what you're occasionally forced to do.
My second problem is with the Gamecube version. I saw on Youtube the side quest with Ada Wong and I was hugely disappointed when I realized the GC version did not have it. Not a big deal for some but it looked like an interesting feature.
Even so, RE4 is great and if every RE fan should play it, I say every gamer should play it.