In general the '07-08 G35's were very good cars. Do you know the maintenance history of this vehicle? If not then I would suggest looking into a transmission and rear diff fluid change. If the drive belt has not been replaced then I would consider that as well. Check filters and also look to replace the cabin filter as well (really easy to do). Check pads and rotors....if brake fluid is dark go ahead and change that too.
Reliability of these cars is based upon care. If it has been maintained then it's good for a long time.