NG was one of the toughest games of the last generation; in the top 5 in terms of difficulty, I think. It's right up there with DMC 3 (NOT the SE), Stuntman, Shinobi, and Viewtiful Joe. So don't be surprised if Sigma kicks your ass every now and then.
I beat the game on Normal, and considering I'm not the greatest at games like this, I considered that a major accomplishment (also beat DMC 3 on "Normal," which was actually Hard). I'm sure Sigma is every bit as hard as the original NG, despite the new weapons you have. I played the demo, and was instantly reminded of how difficult the game is. I don't remember the camera being THAT problematic, though...guess I've been spoiled by better cameras over the past few years.
But it's still a fantastic title, and the original was possibly the best pure action game of the Xbox generation.