From what I understand, many babies can be very particular about what they eat. I mean, for 6 months, he had nothing but formula, and then we give him this strange mushy stuff that he has to eat in a weird way? And now other stuff that tastes different? It's gotta be a shock, and probably one that not a few babies rebel at for awhile.
My son, while not quite as picky, had VERY definite taste buds even at an early age, which surprised me, and we were limited on what he would try, but often he would eat something after two weeks that he refused to eat when it was first tried. Even now, when he will eat most baby foods, we are struggling to move him into to "more" solid food because he doesn't seem to like to try new things.
My advice is just to give him what he'll eat. At the moment, most of his nutrients need to come from formula and/or breast milk, so the baby foods you are giving him, while important, are more to get him into eating solid foods than to give him nutrients he needs. Keep trying each day something different without the baby cereal, and I'm sure eventually he'll realize that it's not bad, and it's something he wants more of.
Good luck!