In the post MMO-RPG world, we tend to make a lot of assumptions about what leveling is and how characters develop as they level, but there's a lot of diversity in how leveling mechanics are managed. Jim, Brian and Tom discuss how leveling has evolved over the years.
Many games purport to have multiple leveling paths that result in differentiated gameplay experiences, but often due to balance or complexity/cost reasons this ideal is not realized. Additionally, social pressure in online games tends to homogenize the character "builds".
Tom loathes auto-scaling zones in open-world games. Jim develops an unhealthy obsession with the TV Tropes website while researching this topic (you have been warned). Everyone agrees that the prospect of losing a level or having XP stolen is terrifying.
Links to referenced items:
Pac-Man, Defender, Bioshock, Robotron 2084, World of Warcraft, Halo, Diablo, CounterStrike, 1942, Bullet Hell, Final Fantasy, Esper, Dungeons and Dragons, Deus Ex: Human Revolution, Dark Souls, Journey, Amalur:Reckoning, Torchlight, Diablo III, Elder Scrolls, The Saga of Olaf, EvE Online, Guild Wars, Anti-Grinding - TV Tropes, Palladium Books, Rifts, Bushido Blade, Fable, Day Z, A Being of Indescribable Power, Killzone Three, Doom, Half Life Two, World of Commanders.