First up, I would like to propose two axioms about old school character creation:
1) What makes a Fighting Man a Barbarian, a Knight, or a Gladiator is the way it is played, not the mechanics behind it.
Old school games rely heavily on player skill, imagination, and creativity. The mechanics are meant to be a spring board for player to do what ever they want. In contrast, newer school games define classes (or whatever they might be called) by the mechanics themselves. This may have the illusion of player skill, imagination, and creativity; however, when mechanics define a character, there is always certain mechanical paths that are going to take advantage of the system better than others. Thus, imagination and creativity are actually stifled, not encouraged.
For Example: Champions seems to have old school credentials, given that it was originally published in 1981. However, I do not classify it as an old school game. One reason for this is that mechanics entirely define the character in Champions. My character may be able to produce fire, but unless I've bought a power that allows me to either raise the temperature in an area or light up an area, my character can do neither of these things. In addition, virtually every character I ever created for Champions (and I played a lot of Champions) had a Dex of 23. Mathematically, this was the most efficient Dex a character could have, and it was just too expensive to do anything else.
For Example: In 3.5, Bards have the class ability Bardic Knowledge. They roll and are able to learn a random bit of info about a particular aspect of their game world. If a Bard has the skill Knowledge (History) with five ranks or more, the Bard receives a +2 on Bardic Knowledge rolls. This mechanically punishes players who want to have Bards with other specialties and virtually guarantees that every 3.5 Bard is going to have five ranks of Knowledge (History).
2) The longer it takes to create a character, the heavier the mechanical burden exists in a game to prevent character death.
Old School games are comfortable with character death. I've written on this before. One reason for this is that characters are so easy to create, that one doesn't have to spent a lot of time out of game to replace the dead character. Sometimes, it is as easy as taking over a henchman. In contrast, games that require a lot of time in character creation balk at having players have to go through that effort again.
For Example: In Champions, it is very difficult to die. Every character has both Stun and Body. The vast majority of attacks can only penetrate standard defenses to do Stun, not Body. Thus, the end of combat results in unconsciousness, not death.
For Example: 3.5 has Challenge Ratings. Every encounter is rated to help guarantee the players will not get in over their heads.