You should add timer and a sand clock that player can pickup to
reverse the time (say player has only 5 seconds out of 200 to finnish
the level, he picks up the sand clock and he has 195 secs left...);
and also fruit that can be pickedup to gain points; also you could add
jump pads that push you 3 fields forward if you go over them;
and also jumping key-binded - to jump over holes, heated fields etc...
Enemies can be really simple without AI (good news for you is it?),you
can simply add some moving cactus or floating daggers that move for
a couple of fields up-down or left-right.Try to put the game in the open
space or atmosphere or use lighter textures for walls.It looks too dark.
Do some ice fields where your ball won't be controllable, it should just
skide towards front until it reaches safe (or death)...Do an effect to
rotate the map when you rotate the ball, if you are doing rotation.
But in case you do all i've said,you should call your game smtn like
Kula World 2 or Rollaway 2 or Kula Quest 2; and probably pay
some fees to certain Japanese developers
For many good ideas visit
http://kulaworld.com/,and find
an iso of this game for PS1 emulator to see how it should go.
Good luck, you have great idea, and your genre pick is ok too,
if you can get physics well.BTW - Do a better texture of the ball