In before the Far Cry, there were two kinds of FPS-es. The ones that used the Quake 3 (IDtech 3) engine and the ones that used the Unreal ones. And then, out of nothing came Crytek and roflstopmed Doom 3 and its claustrophobic corridors. Ladies and gentlemen, this is the game that showed Carmack that one can make real time shadows with nearly unlimited view distance.
Enough of the history lesson. Far Cry as a game was quite revolutionary back in its time (and still is). Mostly sandbox like, you can chose which path you take. The graphics are awesome (even in 2009), the AI is pretty smart -altough a few times a brick can outsmart it- and the level design is just amazing. Quite a few times you can reach your goal on foot through the jungle, on a conveniently placed boat/jeep and even on gliders!
The one letdown in the game is the introduction of those mutant things. For me, they totally threw off the gameplay for many reasons. They have no AI -if you get within a certain radius they go for you-, they instant die when touching water and simply, they are just ridiculously overpowered compared to the mercenaries.
The multi-player is pretty great. Reminds me of Enemy Territory. Haven't played it in ages, so I have no idea if its active at all.
All in all, buying this game is a nobrainer for anyone who likes FPS games.
PS.: The big dual rocket launchered mutant thingies weakspot is not that glowing bit on their chest -they take less damage there-. Aim for the head!