could be better and could be worse
I don't like the way you're doing the number of lives, mostly because there doesn't seem to be a point to it. If you decide to leave it in, could you label them? Just add "Lives: " before the three balls in the corner? Other than that, the game is alright. It's not flashy or exciting, but works for casual play and is different enough from the "standard" matching blocks games I've played to make it worth a few minutes of my time.
If you want to spice it up, try adding a timer/Tetris mechanic to it. If more balls can't be added when the timer expires, you lose. People will catch on quickly and it justifies the three lives.
The control is nice and responsive and I like the way it's set up. Bejewled with magnets I think sums up what the game is going for. What needs to be added though is either an announcer voice like in Bejewled Blitz announcing any combos you get. That or music. I think techno would be a good choice because it makes you want to go faster. Or maybe to make it even more like Bejewled, have there be super balls that blow up everything surrounding them or just add more color to the background. I'm thinking Cyan or something like that, just anything other than grey or one of the colors of the balls. And make the giant magnetic ball give off little jolts of electricity or making it look more magnetic by giving it a chrome color. Just a few thoughts to improve the game!
Pretty fun and addicting, not bad.
Interesting, but not new idea :D might i suggest that you have the balls contact a bit more, sometimes the bounces throw the clicks off