Some of the shots, the ISO looks a bit high. if you can stick with 200, you'll get less grain, I go even lower on some of the macro shots.
Did you shoot in manual mode? its a bit tricky when you first are starting off so you might want to work your way up to it.
I actually write my preferred settings down on a clip on slate, in case im too narced out to remember
you can also get some good pics in shooting aperture mode, adjusting the brightness up and down....only one setting to fiddle with.
i would highly suggest you get a copy of lightroom for some additional editing options, post edit processing.
I also suggest you invest in a single strobe to start with, shoot in until TTL mode to get used to it. it really helps bring out the pop and clarity of UW pics.
All said, not to bad of pics. It's amazingly hard to focus and take pics at the same time, lots to process.
suggested reading:
http://www.uwphotographyguide.com/canon-s90-g11-underwater-settings
happy diving