Falz, - I can agree with you about the Goldfish 'fish', they are beautiful! (Though I find their desire to stay at the sides of the tank irritating), - but I can not agree with you about the rest of the GA tank.
It's a matter of personal opinion isn't it? - To me, that 'rock' in GA is a poorly made fibreglass molding, and I don't like the plastic/dead blurry looking plants. - How you can prefer the blurry background of GA over the pin sharp detail of the coral in MA, I find surprising.
A 3D 'effect' is not an end in it's self, IMO. - I find Jim's 2D corals infinitely more realistic than the so called 3D plants/rock in GA. I have downloaded most of the other fish screensavers over the past few years.
NONE have yet reached the standard of MA! - Two recent ones, AquaZone and AquaGarden, have some nice details, but require much work still to be done on fish movement, (AquaZone), and fish/plant avoidance, (AquaGarden).
ps,
For me, Sharks has got serious perspective problems! - The most realistic is still MA, but keep an eye on AquaGarden!