Wow! A classic in the making.. simple, yet the original physics of it makes it great fun, well done!
Reminds me of that 'football-bouncing-keep-em-up' craze.
So - and I presume you're going to take it further - may I suggest some things:
Variation in levels - when a certain number of targets hit is reached, the level ends and the next level is started with the smallest mace. Levels become more complex such as moving/bouncing targets, walls, multiple targets, targets that need to be hit mutiple times/split apart a la asteroids. A bit like how arkanoid compares to breakout. A level designer would also increase the logevity. Different backgrounds for each level would give a feeling of progress.
Some power ups for immediately increasing/decreasing the size of the mace or maybe the weight/density too, changing the gravity parameters, altering the elasticity, perhaps even multiple maces.
Three lives, let the game progress further.
Slightly better feedback, perhaps via sound, of how stressed the elastic is - the stress bar could be more prominent, especially when red.
Again a little more feedback on how long you have left to make a combo - perhaps a bar at the top that slides down in the time remaining to make a combo.
The visuals are great (apart from the few rough/pink edges that are always going to happen in the early stages of development) mainly due to their fluidity. I'd like to see a bit more drama when making high combos, such as more particle effects, just to get a bit of 'reward'.
Timer - I don't actually think you need the game timer - incidentally it doesn't seem to work (goes negative) on the version I'm using anyway.
Good luck with your project - I expect zillions of clones of your idea will appear pretty soon - probably flash based games spread 'virally' through email.
