Quoted from bigdaddy1:
Extra Ball is the only reward after making S-P-E-C-I-A-L or 3 in line (NO CREDITS are awarded when any of these two sequences are completed).
"Free Games" (replay credits) are won by reaching point levels, match OR - getting the 4 corners on the square. That last special is also adjustable for 1, 2 or (I think) 3 games. That is a cool feature as there is a risk-reward element in trying to go for 4-corners and maybe passing up shots for the extra ball via 3-in-a-row.
Very fun - and fast - game. My has been on 'loan' to a friend for a few years. I need to get it back!