Why not add new blocks, such as wilds or bombs? Try something like the special blocks in the later Bejeweled games, only with numbers. How about an option to change the board size? Maybe a slowly charging power that lets you knock out a single block? Don't get me wrong - I love Chain Factor, but not introducing any variation seems like a waste of potential.
You have the same scoring system, the same number of drops til the next level, and even the same cracks for the gray blocks. Why not change *something*?