Li Shenron
Legend
What rules of 3e do you really like a lot and wish they were ported to 4e (adjustments notwithstanding)?
It doesn't matter whether you think it's unlikely/impossible they will be maintained... just what you wish!
For me it's at least:
Feats:
- in the sense of a system of "special abilities" that a can be taken every X level to customize your character
- I like the idea that feats are approximately equally useful
- I also like the prerequisite ideas for feats, that create "feat chains"
Skills:
- for me it's been the best system for "anything else than fighting and casting spells"
- very simple mechanic, fast to use
- high degree of customization
- I also like how class skills list help separating the roles of the different classes, without completely barring uncommon characters
I think these 2 ideas were among the best things introduced by 3e.
It doesn't matter whether you think it's unlikely/impossible they will be maintained... just what you wish!

For me it's at least:
Feats:
- in the sense of a system of "special abilities" that a can be taken every X level to customize your character
- I like the idea that feats are approximately equally useful
- I also like the prerequisite ideas for feats, that create "feat chains"
Skills:
- for me it's been the best system for "anything else than fighting and casting spells"
- very simple mechanic, fast to use
- high degree of customization
- I also like how class skills list help separating the roles of the different classes, without completely barring uncommon characters
I think these 2 ideas were among the best things introduced by 3e.