You need a reasonably modern machine to run this game (Vista or Windows 7, and a decent DX10 graphics card) but the result are remarkable. At this price (£5.99 on Amazon at time of writing) it's an absolute steal. If you like first person shooters, or even if you are just fascinated by the developments in computer graphics, you should buy this as a treat. The fact that you get around 100 hours of gameplay at such a bargain price is icing on the cake.
Just Cause 2 gives you a complete subtropical archipeligo of islands to explore, there are no levels or loading screens (except for targetted missions) the world is open to explore, with each town village or military base providing its own level-like challenge.
The graphics vary between good (local textures in towns) to true eye candy. From natural scenery and man-made structures of truly massive scale, down to little details like day/night cycles (nightime views of the cities are spectacular) there are times when the sheer visual appeal of a scene from a high-flying plane (or low flying parachute) makes you want to just stop and admire the view. Just Cause is not about realism however, it's about ludicrous (but fun) OTT action, and things like flying a plane into an oil refinery as the start to a day at the office!
It's not perfect, there are a small number of bugs and glitches, but nothing like the problems of early releases some other more well-known first person shooters. It is also dependent on Steam, which is worth knowing as some people have had trouble with Steam. Some of the gameplay can get repetitive, but as a largely free-form game if you don't what's happening, you can choose to do something deranged (like stand on top of a jet fighter for a free ride, or crash a wheeled tank into a gas storage vessel) to mix things up a bit.
Whatever its minor faults, this is a game that deserves to be considered in the same breath as some of the greats, the fact that it seems to have fallen from high-profile visibility fairly quickly is a great shame for the developers, but it means you can pick up a great game at a bargain-basement price which is pretty cool for us customers.