Generally, the closer to le Drus you take a line, the steep and more difficult they become. I have been down the Rectiligne Couloir, on the upper side of the right of the two parallel ridges, it ws a pretty good line, steep in places. The main route down is not so serious, although prone to sliding in the instances that it is totally tracked out. Depending on the cover, one or two sections of very short glacier ice sliding are required, nothing bad though. The best strategy on these very short sections, when you can't go around, is to forget you have edges on your board and slide the ice lump like a rail. What ever you do, don't try and stop or you will go on your bum. Further down the route is important to ride towards skiers left to ensure that you end up in a good spot for accessing the Mer de Glace. The popular word is to aim for a dead larch tree, but I think that has disappeared. The last section of the ride is down a genuinely steep and rocky face onto the Mer de Glace. I pity you if the cover is poor as it is a tangle of shrubs and rocks and both times I have been down, it has been moderately hard work. If you enter this short face in the wrong spot then you get to practice your cliff drops.