Of all the many movies that have been made based on Leroux's novel, the two that most closely follow Leroux's description are the 1925 silent film version starring Lon Chaney (who created the special effects for his face himself!) and the 1987 animated version.
How did Erik really look? Based on numerous clues in Leroux's novel, Erik would have lived sometime between 1821 and 1885. Thus, photography was invented early in Erik's life, but but handheld cameras were invented very near the end. Considering his feelings about his own appearance, it is unlikely he would have allowed himself to be photographed. Considering how few friends he seems to have had, it's entirely unlikely that anyone would have wanted to photograph him anyway. Add to all this that he was fictional (although many do claim he might have been based on a real person, or else might have been a conglomeration of a couple of real people, another fictional character and a few wild imaginations of Gaston Leroux) and it really makes it impossible to say for certain how he looked.
Of course, we have the description that Joseph Buquet provided in Leroux's novel: "He is terribly thin and his dress suit floats over a skeletal framework. His eyes are set so deeply that it's hard to see their pupils. In skin is stretched over his bones like that of a drum. It's not white at all, but an ugly yellow; there's little of his nose that, seen in profile, it's invisible, and the absence of that nose is something horrible to see. And all he has in the way of hair is three of four long brown locks hanging down in front and behind his ears" (Wolf, 30).
We have Leroux's description from Christine: "Imagine if you can the mask of Death with its four black hole that are its eyes and nose and mouth coming suddenly to life to express the sovereign anger of the devil. And no expression coming from its eye sockets for... his fiery eyes can only be seen in the dark" (Wolf, 180).
Finally, we have the words of the enigmatic Persian Daroga: "When he risked going out in public, he would cover his horrible nose-hole with a papier mậché nose complete with a mustache, which did not at all keep him from looking macabre since, as he went by, people behind him would say, 'There goes the grim reaper.' Still, the nose made him almost--I stress almost--bearable to look at"(266).
In truth, however, no one can be entirely sure.
For more images of what Erik might have looked like, visit El's DA page or check out any of these other great Phantom-fan artists: