The mystery about games. Especially fighters and action games. Move lists had to be discovered and memorized. Now there are easy to find videos on the internet. Hell I remember spending tens of hours on the Tony Hawk PS1 demo not having any idea that the game had special moves. I read it in a Gamepro or Gamefan and it blew my mind.
Lack of Internet also lead to many unknown huge games. Speaking of Tony Hawk, when I asked my EB Toys or GameStop associate, idr which store it was, if they had THPS in stock his response was basically laughter because of course they had copies, who'd wanna buy Tony Hawk you moron. Low and behold the game blew up huge. Just doesn't seem like that happens much at all anymore.
Cosmetics you'd unlock via cheat codes or by playing. My all time favorite game is probably MGS and you could unlock a tux to play the game in. Nowadays that'd be $5.
Also, car combat games.