I am assuming that these other Wi-Fi devices (around the house) used to connect just fine before the lightning strike? If so, it may be possible that the Extreme was damaged.
However, before assuming so, I would take some Signal-to-Noise Ratio measurements at different location where you want to gain access to the wireless network to see how well the Extreme is providing a signal with enough bandwidth to be useful.
Please check out the following AirPort User Tip for details on how to take these measurements. Please post back your results.