Character classes are not necessary, but I agree with you that they're better than generic life levels. Even better is a granular attribute & skill level system, such as found within the World of Darkness system (Mage: The Ascension, Vampire: The Masquerade, etc.). So strength, stamina, programming, statistics, and so forth each have their own level. When you get advanced enough in level in a narrower skill area like statistics, you can sub-specialize that skill. But I think we don't need to worry about special cases like that for now.