Most lines running average 80% of normal operation, due to the power shortage. Trains run in a special timetable, so don't rely on the normal time schedule.
JR Narita Express is still not in operation. People heading from/to Narita Airport should take the limousine bus or the Keisei Skyliner.
The Tohoku SHinkansen will take until the end of April to resume operation, as it has taken damage to it's rails by the earthquake.