As much as I hate to sound like a fanboy, this game really is worth the purchase. The campaign is meaty, a good length and the choice of stealth/all guns blazing makes it really worth playing through. Story has been updated to one that, albeit isn't better than the original, is far more streamlined and suitable for a video game.
Multiplayer is awesome as soag already said. I haven't had too much time to play it but I'm loving it when I do. Trying to get my Kill/Death Ratio up to 2.00 (currently at 1.90!). Really good fun and not even Black Ops multiplayer has deterred me from using my free time playing this.
So please buy. Add me as a friend. And let us pwn all!