Unlocking something new with in-game currency or by doing something in a way that feels like you earned it, no loot boxes, microtransactions, or being showered with items for no apparent reason. Good examples of this are the classic NFS/Midnight Club games (new cities/areas, car parts), Gran Turismo (up until 4, maybe 5), Mario Kart (new circuits and karts), classic Zeldas (a new dungeon item), or classic RPGs like Chrono Trigger and the leveling-up mechanic.
The worst examples I can think of are mobile games and Forza Horizon. It's almost like they read somewhere that "the brain's reward system goes haywire when people get a reward" and apply that to the game without any understanding about creating a sense of progression. It feels meaningless when I get random stuff in loot boxes or when I finish a race in Forza Horizon and I get 300 cars and 200.000 credits.