When I think about making characters, I find myself drawn to particular things now (some of which I have discussed in the past.
When given a choice between being able to jump into the action and customizing an exact character, I now prefer the former. I had long term relationships with Hero System in the 80s - 90s and with 3rd edition in the 2000s, so I understand the appeal of custom character builds. But I find that custom builds annoy me more than they amuse me. Plus, as a GM, teaching new players how to build effective characters and managing differences in effective character builds vs. ineffective ones has always bugged me.
Besides, it's easier to feel okay killing somebody's character if they can have a replacement ready before the next big encounter.
2. Meaningful Choices
The joy of old school class system like OD&D and T&T is that classes define what you contribute to the game. The archetypes In Feng Shui similarly give characters a special role at the table. 4e even does a decent job of this, though I think the large number of class, race, build, feat, etc. options water this down.
In short, I think it's easier to get into the game and the group dynamic if it's clear what you contribute, where you shine, and why you need others to help you. It's harder to learn how to do this in an entirely open-ended system. Given a billion choices, it still only matters which one are effective in achieving your goals. For that to be true, it helps to have significant measures of goals and differences.
This leans me to consider class or class/race (D&D, T&T, or at the heart of it World of Darkness) or archetype (Feng Shui, Talislanta) systems as particularly useful models.
3. Relatively Simple
By this, I mean that it shouldn't take Herculean efforts to explain task resolution and that your character sheet should't be so complex that you have a hard time figuring out you skills/powers/abilities on a regular basis. It shouldn't make you head ache to figure out your turn. I tend to find abstraction a good thing and slavish detail spent on simulation tedious and off-putting.
How to preserve these things in a system without alienating contemporary gamers is my challenge.