With iOS 6, I had no issues with the camera from the lockscreen. Pull up on the icon, and it would open. This was very fast and easy to use.
With iOS 7, this is much much harder. I don't know if this is because they added Control Center, and now there's a lot of swiping target areas in a small space, but I find it incredibly difficult to engage the camera. It will either do nothing, or the camera will open up about half way and then fall back to the bottom. I've tried swiping quickly, and slowly. Sometimes I can get it to succeed if I drag it all the way to the top, but it's totally unreliable, and making me crazy. I've missed a number of great photo opportunities because of this!