USB wireless adapters good for games?

It also depends on the router but it will likely make no difference. You do not need speed for games you need clean transmission and that is more a condition of the environment you run it in rather than the brand of equipment you run.

802.11n tends to take fewer errors than 802.11g because of how the data is encoded but if you have other transmitters on the same channels you will have issues no matter the encoding.

Bottom line no wireless adapter can be considered "good" for gaming. If you get lucky and nobody else is using the radio frequencies it will work well but if you have someone else , which is very likely, using the radio you will get random stalls due data retransmission