Far Cry is in essence a very good looking and expertly crafted game that fails when it comes to making the player enjoy playing it. This game runs very well on modern PCs, and actually still looks good despite being about 5 years old. The controls are pretty fluid, even though they do take some getting used to, and the gunplay is actually somewhat entertaining.
However, covering the basics succesfully rarely constitutes a game that's thoroughly good. Far Cry is not thoroughly good, it's simply good and simple fun. The gameplay falls because some of the elements the huge jungle surroundings enable are not properly executed. Sneaking up to people is very hard, in the latest patch the enemies can see you through tents and trees for example, and stealth is actually diminished entirely about 2/3 through the game with the introduction of a new enemies that can pretty much only be killed by you running into them and slashing them apart with bullets.
Regarding the change in enemies, the other major problem with Far Cry is that it creates variety to it by using the wrong methods to do so. First of all, in order to keep you interested Far Cry throws these mutated supersoldiers at you when you have about one third of the game to go, which essentially makes it a rail shooter. I don't think variety should be achieved by diminishing the game that previously existed by destroying it's wonderful opening concepts, and that's what FC does in this respect. Also, one major problem is the lack of progress, or moreso the feel of it. You don't really feel like you're progressing throughout most of the game. The storyline is rather blatantly just an excuse for you to blow stuff up that it doesn't suffice as a driving force to keep you going on your adventure. The game features no roleplaying elements such as improving stats, and the surroundings are pretty much the same jungle/tunnel-mixes throughout. Hence, there's really no variety in Far Cry, and the little there is is created by picking up a new weapon, and mutants coming in. This doesn't make the player feel like he's advancing any where at any time, so it feels sub-par and Far Cry doesn't give you a sense of accomplishment.
But that doesn't mean it isn't possible to enjoy it. Like Painkiller, Far Cry is best enjoyed as a once-a-week treat for action fans. The action is good as long as you play it rarely enough. Would you pay 10 bucks for having a few hours of fun a week for a few months? I would, but I actually already own this one boxed. If you're dying for some action, get this or Painkiller, they're both well worth the money here at GOG.com.