Very impressive shots for a beginner, you must have a lot of natural talent! Not to mention lots of ambient light! However, if you want to take your pics to the next level, I would say you need to shoot manual mode, and external strobes are absolutely essential, unless you are blessed with a lot of ambient light. Shooting RAW helps a lot too, because you can fix white balance later quite easily.
I started with a SeaLife, and flailed around in automatic mode for 2 years. Once I took an underwater photography course where basically the emphasis was to shoot in manual mode, my shots improved a lot. The compact Canons (i.e., G15, S100, S110, etc) give better quality shots, especially for macro, and are easy to use in manual mode, and shoot RAW. I would definitely recommend one of these high-end compact Canons over Sea-Life.
I also agree with Dandy Don to not even try taking pictures underwater until you are very comfortable with your buoyancy, etc.