The G3220 will beat the Q6600 in games that do not utilize the 4 cores a Q6600 has. So it will definitely perform better in games that only use one or two cores.
But if you are using all four cores, a Q6600 should be more powerfull. If you already own a Q6600 and want to upgrade to a pentium i'd say it isn't worth it. But if you have to choose between the two you should choose the G3220.