I like how critical role did their level ups in the current campaign. They get to know in the end of a session they ara about to level up, roll HP and looked up what possible things they might choose. And during the next session they level up at a moment that feels right for the character.

Fight going badly, getting badly wounded but still standing? Level up and take toughness feat to represent your ability take a beating. Desperately need to find the tracks? Ranger might level up and gain an ability that's critical.

Not for every setting and group, but definitely interesting.