I have just played through once but shot loads of what looked like test tubes, yet still no bonus characters/sounds/art at the end?

I can play the bonus missions. What am I missing here?

The concept art and character viewers are only available if you break certain memory capsules on the side missions. Each time you beat a side mission you get another side mission. There should be a memory capsule in every mission, except for the bonus extra missions that you have to break a certain memory capsule to get. (Yeah I know, it sounds a bit confusing)

and you have to finish the game at least once to unlock all that

Ahh, thanks guys.