Got the game when it came out B, and I have to tell you, it rocks. Is it worth $30? Well, probably not. Unless you get it off EBAY in the $20 range you'll be ok. It's a nice addition to BF2, on top of extra maps (night missions included), you get new weapons, NVG's, a zip line to slide from roof to roof, tear gas (nice effect), gas mask, flash bang, grappling hook, new vehicles and of course new classes including Insurgents, Spetsnaz, British.
Problem? Hardly any servers hosting the BF2: SF goodies.
People are still playing the original maps with the original gear. Making BF2: SF unplayable. Once every blue moon you'll find a good server hosting it, but it's probably not worth the $30 because of this rarity.
See ya on the Battlefield!