About the difficulty, I genuinely recall the developers saying that they didn't knew anyone who had played it through to the end, perhaps it was about the first expansion.
It got poor reviews mainly because it came in the wake of COD1, and it was lambasted for trying to Follow the Leader. Which is true in a sense, but I don't think it's that bad. It still has some Commandos-ness.
As I said it's Hitman, Sniper Ghost Warrior and COD rolled into one game. It has the Spy, the bloody Sniper and the Green Beret, which gives it much more variety than most FPS. It's still an old school game, you can save everywhere(save scumming galore), there is even realistic head bobbing.
It's like Deus Ex light.