Actually the FPS game that started it all for me, so I have to give it some love.
Of course the first two levels of SOF are also the best, and both are in the demo. But for some reason the gore and dismemberment fit right in with the theme and environment of the game .
Here you are not walking through a wonderous valley full of trees and butterflies, slaughtering animals and monsters. In SOF you start out in a cleared out Subway freeing hostages from a street gang of skinhead, tattoo'd thugs with guns. It was brilliant , brutal, but fun. No tactical or military garbage, or team members to order around, just you, a gun, and some a$$ kicking to do (and heads to blow off - quite literally).
As the real life John Mullins, you'll head to a gritty desert slaughterhouse in Africa, an office building in Tokyo, battle on top of a running train, blast your way through sewers and a Siberian outpost, and several other locales. And it's all tied together at a hideout with some ex-Vietnam pals who help to coorindate your mercenary trips and goals.
Mercenaries are cool - they make good video game characters, in a Hitman 47 kind of way, but with fast paced twitchy action. We need more mercenaries these days, and a lot less military and police games if you ask me.
SOF is a classic, you have to appreciate it for what it is, and when it was made at this point - it's still a very fun game, much like NOLF and Deus Ex still are (Quake 2 , Unreal and Lithtech were all incredibly good engines ).
SOF does get repetitive near the end game and the boss fight can be tough to an extent. It can be linear (fine with me) and the AI heavily scripted (but worthwhile), but if you like FPS action games, it's hard to imagine why you wouldn't like this classic. Shooting off arms, legs, heads, and gutting torsos is a guilty virtual pleasure that hardly any games these days do . The violence/brutality of this game is so bad, that it almost makes a statement for non-violence, after doing that for 15+ hours.