As far as what you do in the game, it basically involves exploring locations and fighting your way out. The level designs are very linear and there is little room for exploration, though you will find a few little bonuses if you search around. For the most part, there is only one path that will take you toward finishing a mission, so how much time you spend on getting there is up to you. I would sometimes enjoy getting to explore, while in other missions I wanted to just get them over with.
If you have your PS3 online, you can play this game in multiplayer arenas with other real life players. This can be more fun than any one mission in the single player game, but it's just more of the same first person combat. I had no trouble finding other people to play online.