For me:
Low-scaling numbers (the math between 1st to 36th level isn't much)
36th level

Every level means something to the player's character class
Choosing a race should remain very relevant mechanically from 1st to 36th level
No magic economy and magic items rarely give +X bonuses
Mercenaries, hirelings, henchmen, cohorts, and followers adventuring with you. The words "adventuring company" really means that, not just four PC's.
Hank, Eric, Sheila, Bobby, Presto, Diana, Uni, Dungeon Master, Venger, and Tiamat (okay, just kidding about the gang, but definitely Tiamat).
Boxed sets with rule booklets, dice, tiles, counters (or minis), and character sheets.