The European Mars Express Mission is one day before the first critical phase. In 26 hours the Beagle Lander will seperate itself from the Orbiter and will start to descend into the Marsian atmosphere. Hopefully it will survive the harsh landing. Landing on the Marsian surface was always a gamble. The last NASA mission Mars Polar Lander crashed on the surface because the retrorockets shut off while the probe was still in the air most propably because the sensors in the landing gear detected the touch down to early.
Even the insertion into orbit is still a critical part. Unfortunately the Mars Climate Orbiter burned out in the Marsian atmosphere during the aerobraking procedure. In this case it seemed that a unit conversion problem occured.