Game as it is now is (imho) not yet in playable stage (but then again, you said yourself its just beta).
1) The controls are understandable, maybe just clear the main menu up a bit.
2) The difficulty is ok, there is, however, an exploit - if you bounce the fish off the bottom wall you can avoid the penguins 90% of the time.
3) The game has potential for fun, but atm it shows it is a work in progress.
What i suggest is first add levels. Progression always makes things more fun. I would also add different maps - for example an L shaped field where you HAVE to bounce the fish of a wall etc. Maybe make the background smaller to increase gaming area.
It has potential though, improve the things above and it will be good :)