A very good choice. I was also searching for a family car here in UK last year and after trialling out few German makes including an X5, ended up buying an 04 plate Rx300. It's a treat to drive and even after all these years it does not feel half as old as it's German competition from the same era. Except few nigly bits that were standard problems in the Lexus of those age, such as rattling dashboard occasionally and break pads that burn out quickly, the car is a treat to drive.
Was confused between an IS250 and an RX. Better half voted for Rx and that's what we bought. Surprisingly lexus are not a common sight on UK roads.