Eye candy is all on offer, and that disappoints
The implementation leaves much to be desired though. The textures on the fish are very pixellated and blocky.
There is a limit to the number of fish and/or decorations that can be place in the tank, but the limit doesn't make much sense (or it just isn't described properly). Certainly a tank should be considered a certain amount "full" if a fish is put in, because a fish consumes a certain amount of oxygen and the fish in the tank will compete for resources. But why should a rock or a piece of driftwood consume resources in the tank?
Placement of tank decorations is very buggy indeed, controlling depth of placement (i.e. where in the tank from front to back) is hit-and-miss. Decorations seem to be limited to the middle 60% or so of the tank, it isn't possible to place them on the edges which seems a major oversight.
It's a nice idea for a passive screensaver type display on your TV when you're not actively using the Wii. Unfortunately the poor graphics mar this idea quite badly.