I bought it for about 12.50 a while back, played a few levels, and got bored. But recently I started again at the easiest setting and I have to say that although much of the plot is laughable, and Crytek have yet to live up to Far Cry's promise, I have enjoyed the game more than I expected.
Even in DX9, without the extra downloads, there are some gloriously spectacular scenes and although there are way too many bits where you are in puppet mode while the plot unfolds, some of those sessions are among the most spectacular scenes I've ever seen on my PC.
So I'd say it's worth £7.49. Turn your Bruce Willis mode on, your thinking head off, and enjoy the ride.