I won't actually get around to playing RE4 until later this week, maybe Friday.
I don't think you'll be disappointed in your decision.
I bought my copy of the game on gamecube over the holiday season, and I was completely glued to it for a few weeks while I finished it.
I actually took a week off just to play it (on my projector with a decent surround sound setup, in the pitch dark, alone).
I still recommend getting Shadow of the Colossus the moment you have the opportunity to though. I started playing that at a party at a friend's house, and we stayed up for a whole day just working through the game, together. I hadn't done that since I got the original Resident Evil like 10 years ago.
I wrote a whole essay about RE4 on another website, so I won't repeat that here. However, in summary, I found RE4 to be my favorite game out of many last year, and yet it did several things that I normally hate in an action game (e.g. escort missions, etc). Ergo, it's something of a mystery to me why I liked it so much. Props to Capcom's attention to detail.
Unlike most, I got bored with RE4 a couple chapters in (at the Farm assault, specifically). Constantly worrying about ammo levels and the sluggish controls cancelled out any fun. It looked very nice (on the PS2) and the story was interesting, but it was just too frustrating to play.
But I'll second the praise for Shadow of the Colossus. Unique and definitely worth playing.