To answer your question, in my opinion it starts too slow and progresses too quickly. At the very beginning its starts off a little boring honestly - but before you know it you have missles and puffa fish to avoid. (I would introduce the puffa fish much closer to the start - well before you see missles). Later however it does start to get cool, (lol was that a spaceship?!)
Other constructive things to think about - I had no idea how many hits i could take before death.
The bubbles (on the shark) should only move once you get some speed up. (Again just my opinion! See if others agree on this).
Could be interesting if you grew a little every fifth time you ate a fish.